Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Pre-tax
Unrealized net holding gains and losses arising during the period, net of related offsets	$ 300	$ 350	$ 1,165	$ 1,685
Less: reclassification adjustment of realized capital gains and losses	107	53	245	(156)
Unrealized net capital gains and losses	193	297	920	1,841
Unrealized foreign currency translation adjustments	43	(11)	55	18
Unrecognized pension and other postretirement benefit cost arising during the period	(5)	1	(8)	(6)
Less: reclassification adjustment of net periodic cost recognized in operating costs and expenses	(116)	(30)	(174)	(78)
Unrecognized pension and other postretirement benefit cost	111	31	166	72
Other comprehensive income	347	317	1,141	1,931
Tax
Unrealized net holding gains and losses arising during the period, net of related offsets	(105)	(123)	(408)	(589)
Less: reclassification adjustment of realized capital gains and losses	(37)	(19)	(86)	55
Unrealized net capital gains and losses	(68)	(104)	(322)	(644)
Unrealized foreign currency translation adjustments	(15)	4	(19)	(6)
Unrecognized pension and other postretirement benefit cost arising during the period	3	0	5	3
Less: reclassification adjustment of net periodic cost recognized in operating costs and expenses	41	10	61	27
Unrecognized pension and other postretirement benefit cost	(38)	(10)	(56)	(24)
Other comprehensive income (loss), Tax	(121)	(110)	(397)	(674)
After-tax
Unrealized net holding gains and losses arising during the period, net of related offsets	195	227	757	1,096
Less: reclassification adjustment of realized capital gains and losses	70	34	159	(101)
Unrealized net capital gains and losses	125	193	598	1,197
Unrealized foreign currency translation adjustments	28	(7)	36	12
Unrecognized pension and other postretirement benefit cost arising during the period	(2)	1	(3)	(3)
Less: reclassification adjustment of net periodic cost recognized in operating costs and expenses	(75)	(20)	(113)	(51)
Unrecognized pension and other postretirement benefit cost	73	21	110	48
Other comprehensive income, after-tax	$ 226	$ 207	$ 744	$ 1,257