Consolidated Statements of Comprehensive Income (unaudited) (Parenthetical) - 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]
Investments with no other-than-temporary impairment, tax provision (benefit)	$ 10	$ (14)	$ 63	$ 48
Investments with other-than-temporary impairment, tax provision (benefit)	(7)	8	44	(5)
Reclassification adjustment for gains (losses) included in net income (loss), tax provision (benefit)	$ 3	$ (1)	$ 29	$ (1)