Debt and Subordinated Convertible Debentures (Schedule of long-term debt instruments) (Details) (USD $)	3 Months Ended					3 Months Ended																																																											1 Months Ended
	Mar. 31, 2012		Mar. 31, 2011	Dec. 31, 2011		Mar. 31, 2012 Accounts Receivable Securitization Facility [Member]	Mar. 31, 2012 1.9 billion dollar ABL Facility [Member]	Mar. 31, 2012 10 7/8 percent Senior Notes [Member]	Mar. 31, 2012 9 1/4 percent Senior Notes [Member]	Mar. 31, 2012 8 3/8 percent Senior Subordinated Notes [Member]	Mar. 31, 2012 1 7/8 percent Convertible Senior Subordinated Notes [Member]	Mar. 31, 2012 5 3/4 percent Senior Secured Notes [Member]		Mar. 31, 2012 7 3/8 percent Senior Notes [Member]		Mar. 31, 2012 7 5/8 percent Senior Notes [Member]		Mar. 31, 2012 4 percent Convertible Subordinated Notes [Member]	Aug. 31, 1998 Six Point Five Percent Subordinated Convertible Debentures [Member]	Mar. 31, 2012 Subsidiaries [Member] Accounts Receivable Securitization Facility [Member]		Dec. 31, 2011 Subsidiaries [Member] Accounts Receivable Securitization Facility [Member]		Mar. 31, 2012 Subsidiaries [Member] 1.9 billion dollar ABL Facility [Member]		Dec. 31, 2011 Subsidiaries [Member] 1.9 billion dollar ABL Facility [Member]		Mar. 31, 2012 Subsidiaries [Member] 10 7/8 percent Senior Notes [Member]	Dec. 31, 2011 Subsidiaries [Member] 10 7/8 percent Senior Notes [Member]	Mar. 31, 2012 Subsidiaries [Member] 9 1/4 percent Senior Notes [Member]	Dec. 31, 2011 Subsidiaries [Member] 9 1/4 percent Senior Notes [Member]	Mar. 31, 2012 Subsidiaries [Member] 8 3/8 percent Senior Subordinated Notes [Member]	Dec. 31, 2011 Subsidiaries [Member] 8 3/8 percent Senior Subordinated Notes [Member]	Mar. 31, 2012 Subsidiaries [Member] 1 7/8 percent Convertible Senior Subordinated Notes [Member]		Dec. 31, 2011 Subsidiaries [Member] 1 7/8 percent Convertible Senior Subordinated Notes [Member]		Mar. 31, 2012 Subsidiaries [Member] Capital Leases [Member]		Dec. 31, 2011 Subsidiaries [Member] Capital Leases [Member]	Mar. 31, 2012 Subsidiaries [Member] Total URNA and subsidiaries debt [Member]	Dec. 31, 2011 Subsidiaries [Member] Total URNA and subsidiaries debt [Member]	Mar. 31, 2012 Subsidiaries [Member] 5 3/4 percent Senior Secured Notes [Member]		Dec. 31, 2011 Subsidiaries [Member] 5 3/4 percent Senior Secured Notes [Member]		Mar. 31, 2012 Subsidiaries [Member] 7 3/8 percent Senior Notes [Member]		Dec. 31, 2011 Subsidiaries [Member] 7 3/8 percent Senior Notes [Member]		Mar. 31, 2012 Subsidiaries [Member] 7 5/8 percent Senior Notes [Member]		Dec. 31, 2011 Subsidiaries [Member] 7 5/8 percent Senior Notes [Member]		Mar. 31, 2012 Subsidiaries [Member] Total merger financing notes [Member]		Dec. 31, 2011 Subsidiaries [Member] Total merger financing notes [Member]		Mar. 31, 2012 Parent Company [Member]	Dec. 31, 2011 Parent Company [Member]	Mar. 31, 2012 Parent Company [Member] 4 percent Convertible Subordinated Notes [Member]		Dec. 31, 2011 Parent Company [Member] 4 percent Convertible Subordinated Notes [Member]		Aug. 31, 1998 QUIPS [Member]
Debt Instrument [Line Items]
Total debt	$ 5,961,000,000	[1]		$ 2,987,000,000	[1]															$ 230,000,000	[2]	$ 255,000,000	[2]	$ 982,000,000	[3]	$ 810,000,000	[3]	$ 490,000,000	$ 489,000,000	$ 493,000,000	$ 493,000,000	$ 750,000,000	$ 750,000,000	$ 22,000,000	[4]	$ 22,000,000	[4]	$ 38,000,000	[5]	$ 39,000,000	$ 3,005,000,000	$ 2,858,000,000	$ 750,000,000	[6]	$ 0	[6]	$ 750,000,000	[6]	$ 0	[6]	$ 1,325,000,000	[6]	$ 0	[6]	$ 2,825,000,000	[6]	$ 0	[6]			$ 131,000,000	[7]	$ 129,000,000	[7]
Less short-term portion	(371,000,000)	[8]		(395,000,000)	[8]																																																						(131,000,000)	(129,000,000)
Total long-term debt	5,590,000,000			2,592,000,000																																																							0	0
Unused borrowing capacity under facility						5,000,000	868,000,000
Interest rate at end of period						0.90%	2.40%
Average outstanding amount under facility						218,000,000	895,000,000
Weighted average interest rate	0.90%						2.40%
A/R Securitization maximum month-end outstanding amount	230,000,000
Letters of credit outstanding							50,000,000
ABL Facility maximum month-end outstanding amount							982,000,000
Maximum borrowing capacity							1,900,000,000
Stated interest rate								10.875%	9.25%	8.375%	1.875%	5.75%		7.375%		7.625%		4.00%	6.50%
Convertible, conversion price (in dollars per share)											$ 21.83							$ 11.11
Restricted cash held for interest payable	25,000,000		0
Principal carrying amount																		168,000,000
Unamortized discount																		37,000,000
Proceeds from QUIPS																																																																	300,000,000
Liquidation value (in dollars per security)																																																																	$ 50
Subordinated convertible debentures	55,000,000			55,000,000																																																							55,000,000	55,000,000
Face amount												$ 750,000,000	[6]	$ 750,000,000	[6]	$ 1,325,000,000	[6]	$ 173,000,000						$ 1,900,000,000

[1] In August 1998, a subsidiary trust of Holdings (the “Trust”) issued and sold $300 of 6 1/2 percent Convertible Quarterly Income Preferred Securities (“QUIPS”) in a private offering. The Trust used the proceeds from the offering to purchase 6 1/2 percent subordinated convertible debentures due 2028 (the “Debentures”), which resulted in Holdings receiving all of the net proceeds of the offering. The QUIPS are non-voting securities, carry a liquidation value of $50 (fifty dollars) per security and are convertible into Holdings’ common stock. Total debt at March 31, 2012 and December 31, 2011 excludes $55 of these Debentures, which are separately classified in our condensed consolidated balance sheets and referred to as “subordinated convertible debentures.” The subordinated convertible debentures reflect the obligation to our subsidiary that has issued the QUIPS. This subsidiary is not consolidated in our financial statements because we are not the primary beneficiary of the Trust.

[2] At March 31, 2012, $5 was available under our accounts receivable securitization facility. The interest rate applicable to the accounts receivable securitization facility was 0.9 percent at March 31, 2012. During the three months ended March 31, 2012, the monthly average amount outstanding under the accounts receivable securitization facility was $218, and the weighted-average interest rate thereon was 0.9 percent. The maximum month-end amount outstanding under the accounts receivable securitization facility during the three months ended March 31, 2012 was $230.

[3] At March 31, 2012, $868 was available under our ABL facility, net of $50 of letters of credit. The interest rate applicable to the ABL facility was 2.4 percent at March 31, 2012. During the three months ended March 31, 2012, the monthly average amount outstanding under the ABL facility was $895, and the weighted-average interest rate thereon was 2.4 percent. The maximum month-end amount outstanding under the ABL facility during the three months ended March 31, 2012 was $982. In March 2012, the size of the ABL facility was increased to $1.9 billion.

[4] Based on the price of our common stock during the first quarter of 2012, holders of the 1 7/8 percent Convertible Senior Subordinated Notes may convert the notes during the second quarter of 2012 at a conversion price of $21.83 per share of common stock. Between April 1, 2012 (the beginning of the second quarter) and April 13, 2012, none of the 1 7/8 percent Convertible Senior Subordinated Notes were converted.

[5] The fair value of capital leases is determined using the expected present value of the leases.

[6] 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.

[7] The difference between the March 31, 2012 carrying value of the 4 percent Convertible Senior Notes and the $168 principal amount reflects the $37 unamortized portion of the original issue discount recognized upon issuance of the notes, which is being amortized through the maturity date of November 15, 2015. Because the 4 percent Convertible Senior Notes were convertible at March 31, 2012, an amount equal to the $37 unamortized portion of the original issue discount is separately classified in our condensed consolidated balance sheets and referred to as “temporary equity.” Based on the price of our common stock during the first quarter of 2012, holders of the 4 percent Convertible Senior Notes have the right to redeem the notes during the second quarter of 2012 at a conversion price of $11.11 per share of common stock. Between April 1, 2012 (the beginning of the second quarter) and April 13, 2012, none of the 4 percent Convertible Senior Notes were redeemed.

[8] As of March 31, 2012, our short-term debt primarily reflects $230 of borrowings under our accounts receivable securitization facility and $131 of 4 percent Convertible Senior Notes. The 4 percent Convertible Senior Notes mature in 2015, but are reflected as short-term debt because they are convertible at March 31, 2012.