SCHEDULE 13G

Amendment No. 0 
Unisys Corporation 
Common Stock 
Cusip #909214108 


Cusip #909214108 
Item 1:	Reporting Person - FMR Corp.
Item 4:	Delaware
Item 5:	3,729,537 
Item 6:	0 
Item 7:	36,856,506 
Item 8:	0 
Item 9:	36,856,506 
Item 11:	10.675% 
Item 12:	    HC


Cusip #909214108  
Item 1:	Reporting Person - Edward C. Johnson 3d 
Item 4:	United States of America
Item 5:	0 
Item 6:	0 
Item 7:	36,856,506 
Item 8:	0 
Item 9:	36,856,506 
Item 11:	10.675% 
Item 12:	IN 




	SCHEDULE 13G - TO BE INCLUDED IN 
STATEMENTS
	FILED PURSUANT TO RULE 13d-1(b) or 13d-2(b)




Item 1(a).	Name of Issuer:	

		Unisys Corporation 

Item 1(b).	Name of Issuer's Principal Executive Offices:

		Township Lane & Union Meeting 
Roads
		  
		Blue Bell, PA  19424
		  

Item 2(a).	Name of Person Filing: 

		FMR Corp.

Item 2(b).	Address or Principal Business Office or, if None, 
Residence:

		82 Devonshire Street, Boston, 
Massachusetts  02109

Item 2(c).	Citizenship:

		Not applicable

Item 2(d).	Title of Class of Securities:

		Common Stock 

Item 2(e).	CUSIP Number:  

		909214108 

Item 3.	This statement is filed pursuant to Rule 13d-1(b) or 13d-2(b) 
and the person filing, FMR Corp., is a parent holding company 
in accordance with Section 240.13d-1(b)(ii)(G).  (Note:  See 
Item 7).

Item 4.	Ownership

	(a)	Amount Beneficially Owned:	36,856,506 

	(b)	Percent of Class:	10.675% 

	(c)	Number of shares as to which such 
person has:  

	(i)	sole power to vote or to direct 
the vote:	3,729,537 

	(ii)	shared power to vote or to 
direct the vote:	0 

	(iii)	sole power to dispose or to 
direct the disposition of:	36,856,506 

	(iv)	shared power to dispose or to 
direct the disposition of:	0 



Item 5.	Ownership of Five Percent or Less of a Class.

	Not applicable.

Item 6.	Ownership of More than Five Percent on Behalf of Another 
Person.

	Various persons have the right to receive or the power to 
direct the receipt of dividends from, or the proceeds from the 
sale of, the Common Stock of Unisys Corporation.  No one 
person's interest in the Common Stock of Unisys Corporation 
is more than five percent of the total outstanding Common 
Stock.

Item 7.	Identification and Classification of the Subsidiary Which 
Acquired the Security Being Reported on By the Parent 
Holding Company.

	See attached Exhibit A. 

Item 8.	Identification and Classification of Members of 
the Group.

	Not applicable.  See attached Exhibit A. 

Item 9.	Notice of Dissolution of Group.

	Not applicable.

Item 10.	Certification.

	By signing below I certify that, to the best of my knowledge 
and belief, the securities referred to above were acquired in the 
ordinary course of business and were not acquired for the 
purpose of and do not have the effect of changing or 
influencing the control of the issuer of such securities and 
were not acquired in connection with or as a participant in any 
transaction having such purpose or effect.

Signature

	After reasonable inquiry and to the best of my knowledge and 
belief, I certify that the information set forth in this statement 
is true, complete and correct. 

May 10, 2007 			
Date

/s/Eric D. Roiter			
Signature

Eric D. Roiter			
Duly authorized under Power of Attorney
dated December 30, 1997 by and on behalf of FMR Corp. and 
its direct and indirect subsidiaries



	SCHEDULE 13G - TO BE INCLUDED IN 
STATEMENTS
	FILED PURSUANT TO RULE 13d-1(b) or 13d-2(b)



	Pursuant to the instructions in Item 7 of Schedule 13G, 
Fidelity Management & Research Company ("Fidelity"), 82 
Devonshire Street, Boston, Massachusetts 02109, a wholly-
owned subsidiary of FMR Corp. and an investment adviser 
registered under Section 203 of the Investment Advisers Act 
of 1940, is the beneficial owner of 33,478,069 shares or 
9.697% of the Common Stock outstanding of Unisys 
Corporation  ("the Company") as a result of acting as 
investment adviser to various investment companies registered 
under Section 8 of the Investment Company Act of 1940.

	Edward C. Johnson 3d and FMR Corp., through its 
control of Fidelity, and the funds each has sole power to 
dispose of the 33,478,069 shares owned by the Funds.

	Members of the family of Edward C. Johnson 3d, 
Chairman of FMR Corp., are the predominant owners, directly 
or through trusts, of Series B shares of common stock of FMR 
Corp., representing 49% of the voting power of FMR Corp.  
The Johnson family group and all other Series B shareholders 
have entered into a shareholders' voting agreement under 
which all Series B shares will be voted in accordance with the 
majority vote of Series B shares.  Accordingly, through their 
ownership of voting common stock and the execution of the 
shareholders' voting agreement, members of the Johnson 
family may be deemed, under the Investment Company Act of 
1940, to form a controlling group with respect to FMR Corp.

	Neither FMR Corp. nor Edward C. Johnson 3d, 
Chairman of FMR Corp., has the sole power to vote or direct 
the voting of the shares owned directly by the Fidelity Funds, 
which power resides with the Funds' Boards of Trustees.  
Fidelity carries out the voting of the shares under written 
guidelines established by the Funds' Boards of Trustees.

	Pyramis Global Advisors Trust Company ("PGATC"), 
53 State Street, Boston, Massachusetts, 02109, an indirect 
wholly-owned subsidiary of FMR Corp. and a bank as defined 
in Section 3(a)(6) of the Securities Exchange Act of 1934, is 
the beneficial owner of 292,137 shares or 0.085% of the 
outstanding Common Stock of the Unisys Corporation as a 
result of its serving as investment manager of institutional 
accounts owning such shares.

	Edward C. Johnson 3d and FMR Corp., through its 
control of Pyramis Global Advisors Trust Company, each has 
sole dispositive power over 292,137 shares and sole power to 
vote or to direct the voting of 292,137 shares of Common 
Stock owned by the institutional accounts managed by 
PGATC as reported above.

	Fidelity International Limited ("FIL"), Pembroke Hall, 
42 Crow Lane, Hamilton, Bermuda, and various foreign-based 
subsidiaries provide investment advisory and management 
services to a number of non-U.S. investment companies and 
certain institutional investors.  FIL, which is a qualified 
institution under section 240.13d-1(b)(1) pursuant to an SEC 
No-Action letter dated October 5, 2000, is the beneficial 
owner of 3,086,300 shares or 0.894% of the Common Stock 
outstanding of the Company.

	Partnerships controlled predominantly by members of 
the family of Edward C. Johnson 3d, Chairman of FMR Corp. 
and FIL, or trusts for their benefit, own shares of FIL voting 
stock with the right to cast approximately 47% of the total 
votes which may be cast by all holders of FIL voting stock.  
FMR Corp. and FIL are separate and independent corporate 
entities, and their Boards of Directors are generally composed 
of different individuals.

	FMR Corp. and FIL are of the view that they are not 
acting as a "group" for purposes of Section 13(d) under the 
Securities Exchange Act of 1934 (the "1934" Act) and that 
they are not otherwise required to attribute to each other the 
"beneficial ownership" of securities "beneficially owned" by 
the other corporation within the meaning of Rule 13d-3 
promulgated under the 1934 Act.  Therefore, they are of the 
view that the shares held by the other corporation need not be 
aggregated for purposes of Section 13(d). However, FMR 
Corp. is making this filing on a voluntary basis as if all of the 
shares are beneficially owned by FMR Corp. and FIL on a 
joint basis.



	SCHEDULE 13G - TO BE INCLUDED IN 
STATEMENTS
	FILED PURSUANT TO RULE 13d-1(b) or 13d-2(b)
	RULE 13d-1(f)(1)  AGREEMENT

	The undersigned persons, on May 10, 2007, agree and 
consent to the joint filing on their behalf of this Schedule 13G 
in connection with their beneficial ownership of the Common 
Stock of Unisys Corporation at April 30, 2007.

	FMR Corp.

	By /s/ Eric D. Roiter			
	Eric D. Roiter
	Duly authorized under Power of Attorney dated 
December 30, 1997, by and on behalf of FMR Corp. and its 
direct and indirect subsidiaries

	Edward C. Johnson 3d

	By /s/ Eric D. Roiter			
	Eric D. Roiter
	Duly authorized under Power of Attorney dated 
December 30, 1997, by and on behalf of Edward C. Johnson 
3d

	Fidelity Management & Research Company

	By /s/ Eric D. Roiter			
	Eric D. Roiter
	Senior V.P. and General Counsel