Income Taxes (Details 3) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance, January 1	$ 308	$ 211	$ 364
Increases:
Current year tax positions	8	79	2
Tax positions related to prior years	0	24	1
Decreases:
Tax positions related to prior years	(289)	(1)	(152)
Settlements with tax authorities	0	(1)	0
Lapse of statute of limitations	(3)	(4)	(4)
Balance, December 31	$ 24	$ 308	$ 211