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)	$ 730	$ 881	$ 1,056
Unrealized holding gains (losses) arising during the period on:
Investments with no other-than-temporary impairment, net of tax provision (benefit) of $61, $(34) and $(36)	128	(71)	(93)
Investments with other-than-temporary impairment, net of tax provision (benefit) of $36, $(5) and $(23)	69	(9)	(43)
Unrealized holding gains (losses) arising during the period, net of tax	197	(80)	(136)
Less: reclassification adjustment for gains (losses) included in net income (loss), net of tax provision (benefit) of $24, $(10) and $(7)	44	(16)	(10)
Change in net unrealized gains (losses) on investments	153	(64)	(126)
Other, net of tax provision	14	(24)	(7)
Other comprehensive income (loss)	167	(88)	(133)
Comprehensive income (loss)	$ 897	$ 793	$ 923