Debt - Extinguishment (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
	Apr. 13, 2015	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Extinguishment of Debt [Line Items]
Extinguishment of Debt, Gain (Loss), Net of Tax		$ 0	$ 0	$ (65)	$ 0
Notes due 2016 2.75% Interest [Member] | Uncollateralized Debt [Member]
Extinguishment of Debt [Line Items]
Extinguishment of Debt, Amount	$ 626
Extinguishment of Debt, Gain (Loss), Net of Tax	$ (14)
Applicable Treasury Rate Duration For Debt Redemptions	10 years
Basis Points Added To Treasury Rate	0.30%
Notes due 2019 8.5% Interest [Member] | Uncollateralized Debt [Member]
Extinguishment of Debt [Line Items]
Extinguishment of Debt, Amount	$ 329
Extinguishment of Debt, Gain (Loss), Net of Tax	$ (51)
Applicable Treasury Rate Duration For Debt Redemptions	10 years
Basis Points Added To Treasury Rate	0.50%