Income Taxes - Income Tax Expense (Benefit) by Current and Deferred (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Current:
United States federal									$ 0	$ 0	$ 0
State									4	3	1
Foreign									41	33	40
Current income tax provision (benefit)									45	36	41
Deferred, net of changes in valuation allowances:
United States federal									177	(2,941)	(6)
State									27	(246)	(15)
Foreign									(84)	1	(96)
Deferred Income Tax Expense (Benefit)									(120)	3,186	117
Income Tax Benefit (Expense)	$ 33	$ (74)	$ (34)	$ (90)	$ 3,189	$ (16)	$ (18)	$ (5)	$ (165)	$ 3,150	$ 76