Debt (Details) - USD ($) | Apr. 11, 2014 | Sep. 30, 2015 | May. 14, 2015 | May. 13, 2015 | Dec. 31, 2014 |
Debt Instrument [Line Items] | | | | | |
Principal outstanding, net of unamortized discount | | $ 2,832,000,000 | | | $ 3,082,000,000 |
Less: current maturities | | (38,000,000) | | | (263,000,000) |
Long-term maturities | | 2,794,000,000 | | | 2,819,000,000 |
Amended Line of Credit | | | | | |
Debt Instrument [Line Items] | | | | | |
Letters of credit outstanding, amount | | 0 | | | |
Commercial Paper | | | | | |
Debt Instrument [Line Items] | | | | | |
Principal outstanding, net of unamortized discount | | $ 0 | | | 201,000,000 |
Weighted average interest rate (in hundredths) | | 0.49% | | | |
Maximum borrowing capacity | | $ 500,000,000 | | | |
Number of days in which commercial paper matures | | 364 days | | | |
Senior Notes Payable Due 2016 | | | | | |
Debt Instrument [Line Items] | | | | | |
Principal outstanding, net of unamortized discount | | $ 250,000,000 | | | 250,000,000 |
Interest rate (in hundredths) | | 1.15% | | | |
Senior Notes Payable Due 2017 | | | | | |
Debt Instrument [Line Items] | | | | | |
Principal outstanding, net of unamortized discount | | $ 250,000,000 | | | 250,000,000 |
Interest rate (in hundredths) | | 1.40% | | | |
Senior Notes Payable Due 2018 | | | | | |
Debt Instrument [Line Items] | | | | | |
Principal outstanding, net of unamortized discount | | $ 450,000,000 | | | 450,000,000 |
Interest rate (in hundredths) | | 6.375% | | | |
Senior Notes Payable Due 2021 | | | | | |
Debt Instrument [Line Items] | | | | | |
Principal outstanding, net of unamortized discount | | $ 250,000,000 | | | 250,000,000 |
Interest rate (in hundredths) | | 4.50% | | | |
Senior Notes Payable Due 2022 | | | | | |
Debt Instrument [Line Items] | | | | | |
Principal outstanding, net of unamortized discount | | $ 250,000,000 | | | 250,000,000 |
Interest rate (in hundredths) | | 3.60% | | | |
Senior Notes Payable Due 2023 | | | | | |
Debt Instrument [Line Items] | | | | | |
Principal outstanding, net of unamortized discount | | $ 250,000,000 | | | 250,000,000 |
Interest rate (in hundredths) | | 4.00% | | | |
Senior Notes Payable Due 2024 | | | | | |
Debt Instrument [Line Items] | | | | | |
Principal outstanding, net of unamortized discount | | $ 250,000,000 | | | 250,000,000 |
Interest rate (in hundredths) | | 3.70% | | | |
Senior Notes Payable Due 2038 | | | | | |
Debt Instrument [Line Items] | | | | | |
Principal outstanding, net of unamortized discount | | $ 300,000,000 | | | 300,000,000 |
Interest rate (in hundredths) | | 7.00% | | | |
Senior Notes Payable Due 2041 | | | | | |
Debt Instrument [Line Items] | | | | | |
Principal outstanding, net of unamortized discount | | $ 250,000,000 | | | 250,000,000 |
Interest rate (in hundredths) | | 5.95% | | | |
Senior Notes Payable Due 2043 | | | | | |
Debt Instrument [Line Items] | | | | | |
Principal outstanding, net of unamortized discount | | $ 250,000,000 | | | 250,000,000 |
Interest rate (in hundredths) | | 5.125% | | | |
Senior Notes Payable | | | | | |
Debt Instrument [Line Items] | | | | | |
Unamortized original issue discount | | $ (7,000,000) | | | (7,000,000) |
Other Debt | | | | | |
Debt Instrument [Line Items] | | | | | |
Principal outstanding, net of unamortized discount | | 27,000,000 | | | 67,000,000 |
Obligations Under Capital Leases | | | | | |
Debt Instrument [Line Items] | | | | | |
Principal outstanding, net of unamortized discount | | $ 62,000,000 | | | $ 71,000,000 |
Amended Line of Credit | | | | | |
Debt Instrument [Line Items] | | | | | |
Maximum borrowing capacity | | | $ 750,000,000 | $ 835,000,000 | |
Term of revolving credit facility | | 5 years | | | |
Remaining capacity under revolving line of credit facility | | $ 750,000,000 | | | |
Letter of Credit | | | | | |
Debt Instrument [Line Items] | | | | | |
Maximum borrowing capacity | $ 200,000,000 | | | | |
Line of Credit Multi Currency | | | | | |
Debt Instrument [Line Items] | | | | | |
Maximum borrowing capacity | $ 750,000,000 | | | | |
New Line of Credit Multi Currency | | | | | |
Debt Instrument [Line Items] | | | | | |
Remaining capacity under revolving line of credit facility | | 714,000,000 | | | |
Maturity date | Apr. 11, 2017 | | | | |
Letters of credit issued | | $ 36,000,000 | | | |