Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Pre-tax
Unrealized net holding gains and losses arising during the period, net of related offsets	$ 350	$ (813)	$ 1,685	$ (1,306)
Less: reclassification adjustment of realized capital gains and losses	53	18	(156)	304
Unrealized net capital gains and losses	297	(831)	1,841	(1,610)
Unrealized foreign currency translation adjustments	(11)	(22)	18	(77)
Unrecognized pension and other postretirement benefit cost arising during the period	1	7	(6)	15
Less: reclassification adjustment of net periodic cost recognized in operating costs and expenses	(30)	(31)	(78)	(96)
Unrecognized pension and other postretirement benefit cost	31	38	72	111
Other comprehensive income (loss)	317	(815)	1,931	(1,576)
Tax
Unrealized net holding gains and losses arising during the period, net of related offsets	(123)	285	(589)	457
Less: reclassification adjustment of realized capital gains and losses	(19)	(6)	55	(106)
Unrealized net capital gains and losses	(104)	291	(644)	563
Unrealized foreign currency translation adjustments	4	8	(6)	27
Unrecognized pension and other postretirement benefit cost arising during the period	0	(2)	3	(3)
Less: reclassification adjustment of net periodic cost recognized in operating costs and expenses	10	11	27	34
Unrecognized pension and other postretirement benefit cost	(10)	(13)	(24)	(37)
Other comprehensive income (loss), Tax	(110)	286	(674)	553
After-tax
Unrealized net holding gains and losses arising during the period, net of related offsets	227	(528)	1,096	(849)
Less: reclassification adjustment of realized capital gains and losses	34	12	(101)	198
Unrealized net capital gains and losses	193	(540)	1,197	(1,047)
Unrealized foreign currency translation adjustments	(7)	(14)	12	(50)
Unrecognized pension and other postretirement benefit cost arising during the period	1	5	(3)	12
Less: reclassification adjustment of net periodic cost recognized in operating costs and expenses	(20)	(20)	(51)	(62)
Unrecognized pension and other postretirement benefit cost	21	25	48	74
Other comprehensive income (loss), after-tax	$ 207	$ (529)	$ 1,257	$ (1,023)