Debt (Schedule of long-term debt instruments) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Debt Instrument
Total debt	$ 9,138,000,000	$ 9,440,000,000
Less short-term portion	(726,000,000)	(723,000,000)
Total long-term debt	8,412,000,000	8,717,000,000
Line of Credit | $3.0 billion ABL Facility expiring 2021
Debt Instrument
Maximum borrowing capacity	3,000,000,000
Total debt	1,365,000,000	1,670,000,000
Remaining borrowing capacity under credit facility	$ 1,590,000,000
Credit facility interest rate at period end	3.20%
Letters of credit outstanding	$ 37,000,000
Average outstanding amount	$ 1,265,000,000
Weighted average interest rate, long-term	3.10%
ABL Facility maximum month-end outstanding amount	$ 1,373,000,000
Senior notes | 4 5/8 percent Senior Secured Notes
Debt Instrument
Stated interest rate	4.625%
Total debt	$ 992,000,000	992,000,000
Senior notes | 5 3/4 percent Senior Notes due 2024
Debt Instrument
Stated interest rate	5.75%
Total debt	$ 841,000,000	841,000,000
Senior notes | 5 1/2 percent Senior Notes due 2025
Debt Instrument
Stated interest rate	5.50%
Total debt	$ 793,000,000	793,000,000
Senior notes | 4 5/8 percent Senior Notes due 2025
Debt Instrument
Stated interest rate	4.625%
Total debt	$ 740,000,000	740,000,000
Senior notes | 5 7/8 percent Senior Notes due 2026
Debt Instrument
Stated interest rate	5.875%
Total debt	$ 998,000,000	998,000,000
Senior notes | 5 1/2 percent Senior Notes due 2027
Debt Instrument
Stated interest rate	5.50%
Total debt	$ 991,000,000	990,000,000
Senior notes | 4 7/8 percent Senior Notes due 2028
Debt Instrument
Stated interest rate	4.875%
Total debt	$ 1,649,000,000	1,648,000,000
Senior notes | 4 7/8 percent Senior Notes due 2028
Debt Instrument
Stated interest rate	4.875%
Total debt	$ 4,000,000	6,000,000
Capital lease obligations
Debt Instrument
Total debt	66,000,000	67,000,000
Line of Credit | Accounts Receivable Securitization Facility expiring 2018
Debt Instrument
Total debt	699,000,000	$ 695,000,000
Remaining borrowing capacity under credit facility	$ 67,000,000
Credit facility interest rate at period end	2.60%
Average outstanding amount under facility	$ 710,000,000
Weighted average interest rate, short-term	2.50%
A/R Securitization maximum month-end outstanding amount	$ 720,000,000
Collateral amount	$ 767,000,000