Debt and Subordinated Convertible Debentures Debt and Subordinated Convertible Debentures (Narrative) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified			1 Months Ended			1 Months Ended			1 Months Ended			12 Months Ended			3 Months Ended										3 Months Ended
	Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2012 5 3/4 percent Senior Secured Notes [Member]		Mar. 08, 2012 5 3/4 percent Senior Secured Notes [Member]	Mar. 31, 2012 7 3/8 percent Senior Notes [Member]		Mar. 08, 2012 7 3/8 percent Senior Notes [Member]	Mar. 31, 2012 7 5/8 percent Senior Notes [Member]		Mar. 08, 2012 7 5/8 percent Senior Notes [Member]	Dec. 31, 2011 4 percent Convertible Subordinated Notes [Member]	Dec. 31, 2009 4 percent Convertible Subordinated Notes [Member]	Mar. 31, 2012 4 percent Convertible Subordinated Notes [Member]	Mar. 31, 2012 ABL Facility [Member]	Mar. 08, 2012 Before July 15, 2015 [Member] 5 3/4 percent Senior Secured Notes [Member]	Mar. 08, 2012 After July 15, 2015 [Member] 5 3/4 percent Senior Secured Notes [Member]	Mar. 08, 2012 After July 15, 2017 [Member] 5 3/4 percent Senior Secured Notes [Member]	Mar. 08, 2012 Before May 15, 2016 [Member] 7 3/8 percent Senior Notes [Member]	Mar. 08, 2012 After May 15, 2016 [Member] 7 3/8 percent Senior Notes [Member]	Mar. 08, 2012 After May 15, 2018 [Member] 7 3/8 percent Senior Notes [Member]	Mar. 08, 2012 Before April 15, 2017 [Member] 7 5/8 percent Senior Notes [Member]	Mar. 08, 2012 After April 15, 2017 [Member] 7 5/8 percent Senior Notes [Member]	Mar. 08, 2012 After April 15, 2020 [Member] 7 5/8 percent Senior Notes [Member]	Mar. 31, 2012 Minimum [Member] 4 percent Convertible Subordinated Notes [Member]	Mar. 31, 2012 Maximum [Member] 4 percent Convertible Subordinated Notes [Member]
Debt Instrument [Line Items]
Convertible Subordinated Debt, Noncurrent	$ 55	$ 55
Face amount			750	[1]		750	[1]		1,325	[1]				173
Proceeds from issuance of long-term debt			725			722			1,281
Redemption price percent																100.00%	102.875%	100.00%	100.00%	103.688%	100.00%	100.00%	103.813%	100.00%
Redemption purchase price in cash percent					101.00%			101.00%			101.00%
Stated interest rate			5.75%			7.375%			7.625%					4.00%
Hedge transactions cost													26
Hedge transactions cost decreased APIC													17
Convertible note hedge transactions shares (in shares)												15.1
Effective conversion price (in dollars per share)														$ 15.56
Percentage premium over price at issuance														75.00%
Closing price at issuance (in dollars per share)														$ 8.89
Market price per share (in dollars per share)																									$ 40.00	$ 45.00
Convertible equity shares (in shares)																									9.2	9.9
Maximum revolving credit amount percentage															10.00%
Debt terms reference amount to maximum revolving credit															$ 150

[1] In connection with the proposed merger with RSC, on March 9, 2012, Funding SPV issued the merger financing notes. The proceeds from the merger financing notes were deposited into segregated escrow accounts and will be released from escrow subject to the satisfaction of certain conditions, including the occurrence of the merger substantially in accordance with the terms and conditions of the merger agreement and the assumption by a newly formed wholly owned subsidiary of URI, into which URNA will be merged in connection with the RSC merger, of all of the obligations of Funding SPV under the indentures governing the notes and related documentation. The aggregate cash received from the merger financing notes, along with $25 of interest payable on the notes, is separately classified in our condensed consolidated balance sheets as restricted cash. See below for additional detail regarding each of the merger financing notes.