Consolidated Statements of Comprehensive Income (unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 208	$ 479	$ 678	$ 684
Unrealized holding gains (losses) arising during the period on:
Investments with no other-than-temporary impairment, net of tax provision (benefit) of $10, $(14), $63 and $48	27	(33)	133	146
Investments with other-than-temporary impairment, net of tax provision (benefit) of $(7), $8, $44 and $(5)	(15)	13	81	(10)
Unrealized holding gains (losses) arising during the period, net of tax	12	(20)	214	136
Less: reclassification adjustment for gains (losses) included in net income (loss), net of tax provision (benefit) of $3, $(1), $29 and $(1)	4	0	52	(1)
Change in net unrealized gains (losses) on investments	8	(20)	162	137
Other, net of tax provision	3	(5)	15	(16)
Other comprehensive income (loss)	11	(25)	177	121
Comprehensive income (loss)	$ 219	$ 454	$ 855	$ 805