Condensed Consolidated Statements of Comprehensive Income (Loss) (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 291	$ 260
Changes in:
Net unrealized gains on investments with other-than-temporary impairments	(9)	(4)
Net unrealized gains on other investments	(429)	67
Net unrealized gains on investments	(438)	63
Foreign currency translation adjustment	12	11
Pension and postretirement benefits	10	7
Other comprehensive (loss) income, net of tax	(416)	81
Total comprehensive (loss) income	$ (125)	$ 341