Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Pre-tax
Unrealized net holding gains and losses arising during the period, net of related offsets	$ 753	$ 486
Less: reclassification adjustment of realized capital gains and losses	(139)	162
Unrealized net capital gains and losses	892	324
Unrealized foreign currency translation adjustments	22	(42)
Unrecognized pension and other postretirement benefit cost arising during the period	(8)	11
Less: reclassification adjustment of net periodic cost recognized in operating costs and expenses	(24)	(32)
Unrecognized pension and other postretirement benefit cost	16	43
Other comprehensive income	930	325
Tax
Unrealized net holding gains and losses arising during the period, net of related offsets	(263)	(170)
Less: reclassification adjustment of realized capital gains and losses	49	(57)
Unrealized net capital gains and losses	(312)	(113)
Unrealized foreign currency translation adjustments	(8)	15
Unrecognized pension and other postretirement benefit cost arising during the period	3	(3)
Less: reclassification adjustment of net periodic cost recognized in operating costs and expenses	8	11
Unrecognized pension and other postretirement benefit cost	(5)	(14)
Other comprehensive income (loss), Tax	(325)	(112)
After-tax
Unrealized net holding gains and losses arising during the period, net of related offsets	490	316
Less: reclassification adjustment of realized capital gains and losses	(90)	105
Unrealized net capital gains and losses	580	211
Unrealized foreign currency translation adjustments	14	(27)
Unrecognized pension and other postretirement benefit cost arising during the period	(5)	8
Less: reclassification adjustment of net periodic cost recognized in operating costs and expenses	(16)	(21)
Unrecognized pension and other postretirement benefit cost	11	29
Other comprehensive income, after-tax	$ 605	$ 213