Debt (Schedule of long-term debt instruments) (Details) - USD ($)	1 Months Ended		6 Months Ended
	Jun. 30, 2017	Feb. 28, 2017	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Debt Instrument
Total debt	$ 8,215,000,000		$ 8,215,000,000		$ 7,790,000,000
Less short-term portion	(644,000,000)		(644,000,000)		(597,000,000)
Total long-term debt	$ 7,571,000,000		7,571,000,000		7,193,000,000
Loss on extinguishment of debt			$ 12,000,000	$ 26,000,000
Accounts Receivable Securitization Facility expiring 2017
Debt Instrument
Credit facility interest rate at period end	1.90%		1.90%
$2.5 billion ABL Facility expiring 2021
Debt Instrument
Maximum borrowing capacity	$ 2,500,000,000.0		$ 2,500,000,000.0
7 5/8 percent Senior Notes
Debt Instrument
Stated interest rate	7.625%		7.625%
6 1/8 percent Senior Notes
Debt Instrument
Stated interest rate	6.125%		6.125%
4 5/8 percent Senior Secured Notes
Debt Instrument
Stated interest rate	4.625%		4.625%
5 3/4 percent Senior Notes due 2024
Debt Instrument
Stated interest rate	5.75%		5.75%
5 1/2 percent Senior Notes due 2025
Debt Instrument
Stated interest rate	5.50%		5.50%
5 7/8 percent Senior Notes due 2026
Debt Instrument
Stated interest rate	5.875%		5.875%
5 1/2 percent Senior Notes due 2027
Debt Instrument
Stated interest rate	5.50%		5.50%
Capital leases
Debt Instrument
Total debt	$ 67,000,000		$ 67,000,000		71,000,000
Credit facility | $2.5 billion ABL Facility expiring 2021
Debt Instrument
Total debt	1,763,000,000		1,763,000,000		1,645,000,000
Current borrowing capacity under credit facility	$ 700,000,000		$ 700,000,000
Credit facility interest rate at period end	2.70%		2.70%
Letters of credit outstanding	$ 40,000,000		$ 40,000,000
Average outstanding amount			$ 1,200,000,000
Weighted average interest rate, long-term	2.50%		2.50%
ABL Facility maximum month-end outstanding amount			$ 1,800,000,000
Senior notes | 7 5/8 percent Senior Notes
Debt Instrument
Total debt	$ 223,000,000		223,000,000		469,000,000
Face amount	250,000,000		250,000,000
Loss on extinguishment of debt	12,000,000
Senior notes | 6 1/8 percent Senior Notes
Debt Instrument
Total debt	935,000,000		935,000,000		936,000,000
Senior notes | 5 3/4 percent Senior Notes due 2024
Debt Instrument
Total debt	840,000,000		840,000,000		839,000,000
Senior notes | 5 1/2 percent Senior Notes due 2025
Debt Instrument
Total debt	793,000,000		793,000,000		792,000,000
Senior notes | 5 7/8 percent Senior Notes due 2026
Debt Instrument
Total debt	$ 998,000,000		$ 998,000,000		740,000,000
Senior notes | 5 7/8 percent Senior Notes due 2026 | URNA
Debt Instrument
Credit facility interest rate at period end	5.70%		5.70%
Face amount		$ 250,000,000
Proceeds from issuance of long-term debt		258,000,000
Aggregate principal amount outstanding	$ 1,000,000,000		$ 1,000,000,000
Unamortized issuance premium	11,000,000		11,000,000
Senior notes | 5 1/2 percent Senior Notes due 2027
Debt Instrument
Total debt	$ 990,000,000		$ 990,000,000		739,000,000
Senior notes | 5 1/2 percent Senior Notes due 2027 | URNA
Debt Instrument
Credit facility interest rate at period end	5.50%		5.50%
Face amount		250,000,000
Proceeds from issuance of long-term debt		$ 250,000,000
Aggregate principal amount outstanding	$ 1,000,000,000		$ 1,000,000,000
Unamortized issuance premium	3,000,000		3,000,000
Senior secured notes | 4 5/8 percent Senior Secured Notes
Debt Instrument
Total debt	991,000,000		991,000,000		991,000,000
Accounts receivable facility | Accounts Receivable Securitization Facility expiring 2017
Debt Instrument
Total debt	615,000,000		615,000,000		$ 568,000,000
Current borrowing capacity under credit facility	$ 10,000,000		10,000,000
Average outstanding amount under facility			$ 557,000,000
Weighted average interest rate, short-term	1.70%		1.70%
A/R Securitization maximum month-end outstanding amount			$ 616,000,000
Collateral amount	$ 694,000,000		$ 694,000,000