Debt (Schedule of Debt) (Details) - USD ($)	3 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Nov. 30, 2016	Aug. 31, 2016	May 31, 2016	Mar. 31, 2015	Mar. 31, 2014	Oct. 31, 2012	Mar. 31, 2012
Debt Instrument [Line Items]
Total debt	$ 7,790,000,000	$ 7,790,000,000	$ 8,162,000,000
Less short-term portion	(597,000,000)	(597,000,000)	(607,000,000)
Long-term debt	7,193,000,000	7,193,000,000	7,555,000,000
Loss on extinguishment of debt		101,000,000	123,000,000	$ 80,000,000
Accounts Receivable Securitization Facility
Debt Instrument [Line Items]
Unused borrowing capacity amount	$ 57,000,000	$ 57,000,000
Interest rate at period end	1.50%	1.50%
Accounts Receivable Securitization Facility | Accounts receivable facility
Debt Instrument [Line Items]
Total debt	$ 568,000,000	$ 568,000,000	571,000,000
Line of credit facility, maximum borrowing capacity						$ 625,000,000
$2.5 billion ABL Facility
Debt Instrument [Line Items]
Unused borrowing capacity amount	809,000,000	809,000,000
Letters of credit outstanding	$ 36,000,000	$ 36,000,000
Interest rate at period end	2.30%	2.30%
Line of credit facility, maximum borrowing capacity	$ 2,500,000,000.0	$ 2,500,000,000.0	2,500,000,000.0
$2.5 billion ABL Facility | Credit facility
Debt Instrument [Line Items]
Total debt	1,645,000,000	1,645,000,000	$ 1,579,000,000
7 3/8 percent Senior Notes
Debt Instrument [Line Items]
Stated interest rate			7.375%
7 3/8 percent Senior Notes | Senior notes
Debt Instrument [Line Items]
Total debt	$ 0	$ 0	$ 740,000,000
8 1/4 percent Senior Notes
Debt Instrument [Line Items]
Stated interest rate	8.25%	8.25%	8.25%
8 1/4 percent Senior Notes | Senior notes
Debt Instrument [Line Items]
Total debt	$ 0	$ 0	$ 315,000,000
7 5/8 percent Senior Notes
Debt Instrument [Line Items]
Stated interest rate	7.625%	7.625%
7 5/8 percent Senior Notes | Interest expense
Debt Instrument [Line Items]
Loss on extinguishment of debt	$ 65,000,000
7 5/8 percent Senior Notes | Senior notes
Debt Instrument [Line Items]
Total debt	$ 469,000,000	$ 469,000,000	1,306,000,000
Redemption of principal amount of debt		$ 850,000,000
Debt instrument, face amount											$ 1,325,000,000
6 1/8 percent Senior Notes
Debt Instrument [Line Items]
Stated interest rate	6.125%	6.125%
6 1/8 percent Senior Notes | Senior notes
Debt Instrument [Line Items]
Total debt	$ 936,000,000	$ 936,000,000	937,000,000
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%
4 5/8 percent Senior Secured Notes | Senior secured notes
Debt Instrument [Line Items]
Total debt	$ 991,000,000	$ 991,000,000	989,000,000
Debt instrument, face amount								$ 1,000,000,000
5 3/4 percent Senior Notes
Debt Instrument [Line Items]
Stated interest rate	5.75%	5.75%
5 3/4 percent Senior Notes | Senior notes
Debt Instrument [Line Items]
Total debt	$ 839,000,000	$ 839,000,000	838,000,000
Debt instrument, face amount									$ 850,000,000
5 1/2 percent Senior Notes due 2025
Debt Instrument [Line Items]
Stated interest rate	5.50%	5.50%
5 1/2 percent Senior Notes due 2025 | Senior notes
Debt Instrument [Line Items]
Total debt	$ 792,000,000	$ 792,000,000	791,000,000
Debt instrument, face amount								$ 800,000,000
5 7/8 percent Senior Notes
Debt Instrument [Line Items]
Stated interest rate	5.875%	5.875%
5 7/8 percent Senior Notes | Senior notes
Debt Instrument [Line Items]
Total debt	$ 740,000,000	$ 740,000,000	0
Debt instrument, face amount							$ 750,000,000
5 1/2 percent Senior Notes due 2027
Debt Instrument [Line Items]
Stated interest rate	5.50%	5.50%
5 1/2 percent Senior Notes due 2027 | Senior notes
Debt Instrument [Line Items]
Total debt	$ 739,000,000	$ 739,000,000	0
Debt instrument, face amount					$ 750,000,000
Capital leases
Debt Instrument [Line Items]
Total debt	$ 71,000,000	71,000,000	$ 96,000,000
7 3/8, 8 1/4, and 7 5/8 Senior Notes | Interest expense
Debt Instrument [Line Items]
Loss on extinguishment of debt		$ 100,000,000