Condensed 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	$ 144	$ 343	$ 676	$ 618
Other Comprehensive Income, Net of Tax
Net unrealized gains on investments with other-than-temporary impairments	1	3	(3)	7
Net unrealized gains on other investments	23	42	167	586
Net unrealized gains on investments	24	45	164	593
Foreign currency translation adjustment	41	(24)	94	(58)
Pension and postretirement benefits	10	6	22	17
Other comprehensive income, net of tax	75	27	280	552
Total comprehensive income	$ 219	$ 370	$ 956	$ 1,170