Income Taxes U.S. and International Components of Income before Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended																12 Months Ended
	Dec. 31, 2015	[1]	Sep. 30, 2015	[1]	Jun. 30, 2015	[1]	Mar. 31, 2015	[1]	Dec. 31, 2014	[1]	Sep. 30, 2014	[1]	Jun. 30, 2014	[1]	Mar. 31, 2014	[1]	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
U.S.																	$ 2,186	$ 292	$ 704
International																	(618)	(403)	(198)
Income (loss) before income taxes	$ 938		$ 247		$ 362		$ 21		$ 429		$ (634)		$ (27)		$ 120		$ 1,568	$ (111)	$ 506

[1] The sum of quarterly amounts, including per share amounts, may not equal amounts reported for year-to-date periods. This is due to the effects of rounding and changes in the number of weighted-average shares outstanding for each period.