Debt - Short-term and Long-term Debt (Details) (USD $) In Millions, unless otherwise specified	0 Months Ended
	Mar. 11, 2015	Mar. 31, 2015		Dec. 31, 2014
Debt Instrument [Line Items]
Total short-term debt		$ 999		$ 147
Long-term debt, carrying value		5,062		5,005
Uncollateralized Debt [Member]
Debt Instrument [Line Items]
Commercial paper		100		100
Current maturities of long-term debt		851		0
Other, including capital leases		48		47
Total short-term debt		999		147
Long-term debt, carrying value		5,062		5,005
$600 million, 2.75% Notes due 2016 [Member] | Uncollateralized Debt [Member]
Debt Instrument [Line Items]
Long-term debt, stated interest rate		2.75%		2.75%
Long-term debt, carrying value		0		600
$250 million, 5.375% Notes due 2017 [Member] | Uncollateralized Debt [Member]
Debt Instrument [Line Items]
Long-term debt, stated interest rate		5.375%		5.375%
Long-term debt, carrying value		250		250
$131 million, 6.35% Notes due 2018 [Member] | Uncollateralized Debt [Member]
Debt Instrument [Line Items]
Long-term debt, stated interest rate		6.35%		6.35%
Long-term debt, carrying value		131		131
$251 million, 8.5% Notes due 2019 [Member] | Uncollateralized Debt [Member]
Debt Instrument [Line Items]
Long-term debt, stated interest rate		8.50%		8.50%
Long-term debt, carrying value		0		251
$250 million, 4.375% Notes due 2020 [Member] | Uncollateralized Debt [Member]
Debt Instrument [Line Items]
Long-term debt, stated interest rate		4.375%		4.375%
Long-term debt, carrying value		257	[1]	254	[1]
$300 million, 5.125% Notes due 2020 [Member] | Uncollateralized Debt [Member]
Debt Instrument [Line Items]
Long-term debt, stated interest rate		5.125%		5.125%
Long-term debt, carrying value		306	[1]	303	[1]
$78 million, 6.37% Notes due 2021 [Member] | Uncollateralized Debt [Member]
Debt Instrument [Line Items]
Long-term debt, stated interest rate		6.37%		6.37%
Long-term debt, carrying value		78		78
$300 million, 4.5% Notes due 2021 [Member] | Uncollateralized Debt [Member]
Debt Instrument [Line Items]
Long-term debt, stated interest rate		4.50%		4.50%
Long-term debt, carrying value		307	[1]	303	[1]
$750 million, 4% Notes due 2022 [Member] | Uncollateralized Debt [Member]
Debt Instrument [Line Items]
Long-term debt, stated interest rate		4.00%		4.00%
Long-term debt, carrying value		745		745
$100 million, 7.65% Notes due 2023 [Member] | Uncollateralized Debt [Member]
Debt Instrument [Line Items]
Long-term debt, stated interest rate		7.65%		7.65%
Long-term debt, carrying value		100		100
$17 million, 8.3% Notes due 2023 [Member] | Uncollateralized Debt [Member]
Debt Instrument [Line Items]
Long-term debt, stated interest rate		8.30%		8.30%
Long-term debt, carrying value		17		17
$900 million, 3.25% Notes Due 2025 [Member] | Uncollateralized Debt [Member]
Debt Instrument [Line Items]
Long-term debt, term	10 years
Long-term debt, face value	900
Long-term debt, maturity date	Apr. 15, 2025
Long-term debt, stated interest rate	3.25%	3.25%
Long-term debt, carrying value	899	899		0
Effective interest rate	3.36%
Percentage of principal amount to be paid upon redemption	100.00%
Basis Points Added To Treasury Rate	0.175%
$300 million, 7.875% Debentures due 2027 [Member] | Uncollateralized Debt [Member]
Debt Instrument [Line Items]
Long-term debt, stated interest rate		7.875%		7.875%
Long-term debt, carrying value		300		300
$83 million, 8.3% Step Down Notes due 2033 [Member] | Uncollateralized Debt [Member]
Debt Instrument [Line Items]
Long-term debt, stated interest rate		8.30%		8.30%
Long-term debt, carrying value		83		83
$500 million, 6.15% Notes due 2036 [Member] | Uncollateralized Debt [Member]
Debt Instrument [Line Items]
Long-term debt, stated interest rate		6.15%		6.15%
Long-term debt, carrying value		500		500
$300 million, 5.875% Notes due 2041 [Member] | Uncollateralized Debt [Member]
Debt Instrument [Line Items]
Long-term debt, stated interest rate		5.875%		5.875%
Long-term debt, carrying value		298		298
$750 million, 5.375% Notes due 2042 [Member] | Uncollateralized Debt [Member]
Debt Instrument [Line Items]
Long-term debt, stated interest rate		5.375%		5.375%
Long-term debt, carrying value		750		750
Other, including capital leases [Member] | Uncollateralized Debt [Member]
Debt Instrument [Line Items]
Long-term debt, carrying value		$ 41		$ 42

[1] The Company has entered into interest rate swap contracts hedging a portion of these fixed-rate debt instruments. See Note 9 for further information about the Company’s interest rate risk management and these derivative instruments.