Debt (Schedule of Debt) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Sep. 30, 2015	Mar. 31, 2015	Apr. 30, 2014	Mar. 31, 2014	Oct. 31, 2012	Mar. 31, 2012
Debt Instrument [Line Items]
Total debt	$ 8,162,000,000	$ 7,962,000,000
Less short-term portion	(607,000,000)	(618,000,000)
Long-term debt	7,555,000,000	7,344,000,000
Gains (losses) on extinguishment of debt	(123,000,000)	$ (80,000,000)	$ (1,000,000)
Accounts Receivable Securitization Facility
Debt Instrument [Line Items]
Unused borrowing capacity amount	$ 48,000,000
Interest rate at period end	1.10%
$2.5 billion ABL Facility
Debt Instrument [Line Items]
Unused borrowing capacity amount	$ 873,000,000
Letters of credit outstanding	$ 37,000,000
Interest rate at period end	2.30%
5 3/4 percent Senior Secured Notes
Debt Instrument [Line Items]
Stated interest rate	5.75%	5.75%
8 3/8 percent Senior Subordinated Notes
Debt Instrument [Line Items]
Stated interest rate	8.375%	8.375%
8 1/4 percent Senior Notes
Debt Instrument [Line Items]
Stated interest rate	8.25%	8.25%
Debt redeemed	$ 350,000,000
7 3/8 percent Senior Notes
Debt Instrument [Line Items]
Stated interest rate	7.375%	7.375%
7 5/8 percent Senior Notes
Debt Instrument [Line Items]
Stated interest rate	7.625%	7.625%
6 1/8 percent Senior Notes
Debt Instrument [Line Items]
Stated interest rate	6.125%	6.125%
Debt instrument, face amount								$ 400,000,000
4 5/8 percent Senior Secured Notes
Debt Instrument [Line Items]
Stated interest rate	4.625%	4.625%
5 3/4 percent Senior Notes
Debt Instrument [Line Items]
Stated interest rate	5.75%	5.75%
5 1/2 percent Senior Notes
Debt Instrument [Line Items]
Stated interest rate	5.50%	5.50%
4 percent Convertible Senior Notes
Debt Instrument [Line Items]
Stated interest rate	4.00%	4.00%	4.00%
URNA and subsidiaries
Debt Instrument [Line Items]
Total debt	$ 8,162,000,000	$ 7,930,000,000
URNA and subsidiaries | $2.5 billion ABL Facility
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	2,500,000,000.0	2,500,000,000.0
URNA and subsidiaries | Capital leases
Debt Instrument [Line Items]
Total debt	96,000,000	105,000,000
Credit facility | URNA and subsidiaries | $2.5 billion ABL Facility
Debt Instrument [Line Items]
Total debt	1,579,000,000	1,293,000,000
Senior secured notes | 4 5/8 percent Senior Secured Notes
Debt Instrument [Line Items]
Total debt					$ 1,000,000,000
Debt instrument, face amount					1,000,000,000
Senior secured notes | URNA and subsidiaries | 5 3/4 percent Senior Secured Notes
Debt Instrument [Line Items]
Total debt	0	741,000,000
Senior secured notes | URNA and subsidiaries | 4 5/8 percent Senior Secured Notes
Debt Instrument [Line Items]
Total debt	989,000,000	0
Senior notes | 7 3/8 percent Senior Notes
Debt Instrument [Line Items]
Debt instrument, face amount									$ 750,000,000
Senior notes | 7 5/8 percent Senior Notes
Debt Instrument [Line Items]
Debt instrument, face amount									$ 1,325,000,000
Senior notes | 5 3/4 percent Senior Notes
Debt Instrument [Line Items]
Total debt	838,000,000	837,000,000
Debt instrument, face amount						$ 850,000,000	$ 850,000,000
Senior notes | 5 1/2 percent Senior Notes
Debt Instrument [Line Items]
Debt instrument, face amount					$ 800,000,000
Senior notes | Add-on to Senior Notes 6 1/8 percent
Debt Instrument [Line Items]
Debt instrument, face amount						$ 525,000,000	$ 525,000,000
Senior notes | URNA and subsidiaries | 8 1/4 percent Senior Notes
Debt Instrument [Line Items]
Total debt	315,000,000	687,000,000
Senior notes | URNA and subsidiaries | 7 3/8 percent Senior Notes
Debt Instrument [Line Items]
Total debt	740,000,000	738,000,000
Senior notes | URNA and subsidiaries | 7 5/8 percent Senior Notes
Debt Instrument [Line Items]
Total debt	1,306,000,000	1,303,000,000
Senior notes | URNA and subsidiaries | 6 1/8 percent Senior Notes
Debt Instrument [Line Items]
Total debt	937,000,000	938,000,000
Senior notes | URNA and subsidiaries | 5 1/2 percent Senior Notes
Debt Instrument [Line Items]
Total debt	791,000,000	0
Senior subordinated notes | URNA and subsidiaries | 8 3/8 percent Senior Subordinated Notes
Debt Instrument [Line Items]
Total debt	0	740,000,000
Accounts receivable facility | Accounts Receivable Securitization Facility
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity				$ 625,000,000
Accounts receivable facility | URNA and subsidiaries | Accounts Receivable Securitization Facility
Debt Instrument [Line Items]
Total debt	571,000,000	548,000,000
Convertible debt | 4 percent Convertible Senior Notes
Debt Instrument [Line Items]
Total debt	$ 0	$ 32,000,000
Stated interest rate	4.00%	4.00%	4.00%
Debt redeemed	$ 34,000,000
Gains (losses) on extinguishment of debt	(1,000,000)
Interest expense | 5 3/4 percent Senior Secured Notes, 8 3/8 percent Senior Subordinated Notes and 8 1/4 percent Senior Notes
Debt Instrument [Line Items]
Gains (losses) on extinguishment of debt	$ (121,000,000)
Total debt | New Accounting Pronouncement, early adoption effect
Debt Instrument [Line Items]
Debt issuance costs		$ 90,000,000