Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net Income (Loss) Attributable to Parent	$ (46)	$ 282	$ 500
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax, Portion Attributable to Parent	329	154	(615)
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax, Portion Attributable to Parent	(28)	(25)	(13)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	301	129	(628)
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	$ 255	$ 411	$ (128)