Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Pre-tax
Unrealized net holding gains and losses arising during the period, net of related offsets	$ 479	$ 663	$ 901	$ 1,381
Less: reclassification adjustment of realized capital gains and losses	64	11	174	(163)
Unrealized net capital gains and losses	415	652	727	1,544
Unrealized foreign currency translation adjustments	17	7	12	29
Unrecognized pension and other postretirement benefit cost arising during the period	(3)	1	(3)	(7)
Less: reclassification adjustment of net periodic cost recognized in operating costs and expenses	(29)	(24)	(58)	(48)
Unrecognized pension and other postretirement benefit cost	26	25	55	41
Other comprehensive income	458	684	794	1,614
Tax
Unrealized net holding gains and losses arising during the period, net of related offsets	(167)	(232)	(315)	(483)
Less: reclassification adjustment of realized capital gains and losses	(22)	(4)	(61)	57
Unrealized net capital gains and losses	(145)	(228)	(254)	(540)
Unrealized foreign currency translation adjustments	(6)	(2)	(4)	(10)
Unrecognized pension and other postretirement benefit cost arising during the period	2	0	2	3
Less: reclassification adjustment of net periodic cost recognized in operating costs and expenses	10	9	20	17
Unrecognized pension and other postretirement benefit cost	(8)	(9)	(18)	(14)
Other comprehensive income (loss), Tax	(159)	(239)	(276)	(564)
After-tax
Unrealized net holding gains and losses arising during the period, net of related offsets	312	431	586	898
Less: reclassification adjustment of realized capital gains and losses	42	7	113	(106)
Unrealized net capital gains and losses	270	424	473	1,004
Unrealized foreign currency translation adjustments	11	5	8	19
Unrecognized pension and other postretirement benefit cost arising during the period	(1)	1	(1)	(4)
Less: reclassification adjustment of net periodic cost recognized in operating costs and expenses	(19)	(15)	(38)	(31)
Unrecognized pension and other postretirement benefit cost	18	16	37	27
Other comprehensive income, after-tax	$ 299	$ 445	$ 518	$ 1,050