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.