Debt - Extinguishment (Details) (Uncollateralized Debt [Member], USD $) In Millions, unless otherwise specified	0 Months Ended
	Apr. 13, 2015
Notes due 2016 2.75% Interest [Member]
Extinguishment of Debt [Line Items]
Extinguishment of Debt, Amount	$ 626
Extinguishment of Debt, Gain (Loss), Net of Tax	(14)
Basis Points Added To Treasury Rate	0.30%
Notes due 2019 8.5% Interest [Member]
Extinguishment of Debt [Line Items]
Extinguishment of Debt, Amount	329
Extinguishment of Debt, Gain (Loss), Net of Tax	$ (51)
Basis Points Added To Treasury Rate	0.50%