Income Taxes - Income Tax Expense (Benefit) by Current and Deferred (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Current:
United States federal									$ 0	$ 0	$ (9)
State									3	1	1
Foreign									33	40	37
Current income tax provision (benefit)									36	41	29
Deferred, net of changes in valuation allowances:
United States federal									(2,941)	(6)	3
State									(246)	(15)	0
Foreign									1	(96)	6
Deferred Income Tax Expense (Benefit)									3,186	117	(9)
Income Tax Benefit (Expense)	$ 3,189	$ (16)	$ (18)	$ (5)	$ 103	$ (8)	$ (12)	$ (7)	$ 3,150	$ 76	$ (38)