Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Pre-tax
Unrealized net holding gains and losses arising during the period, net of related offsets	$ 444	$ 753
Less: reclassification adjustment of realized capital gains and losses	132	(139)
Unrealized net capital gains and losses	312	892
Unrealized foreign currency translation adjustments	(5)	22
Unrecognized pension and other postretirement benefit cost arising during the period	0	(8)
Less: reclassification adjustment of net periodic cost recognized in operating costs and expenses	(29)	(24)
Unrecognized pension and other postretirement benefit cost	29	16
Other comprehensive income	336	930
Tax
Unrealized net holding gains and losses arising during the period, net of related offsets	(155)	(263)
Less: reclassification adjustment of realized capital gains and losses	(46)	49
Unrealized net capital gains and losses	(109)	(312)
Unrealized foreign currency translation adjustments	2	(8)
Unrecognized pension and other postretirement benefit cost arising during the period	0	3
Less: reclassification adjustment of net periodic cost recognized in operating costs and expenses	10	8
Unrecognized pension and other postretirement benefit cost	(10)	(5)
Other comprehensive income (loss), Tax	(117)	(325)
After-tax
Unrealized net holding gains and losses arising during the period, net of related offsets	289	490
Less: reclassification adjustment of realized capital gains and losses	86	(90)
Unrealized net capital gains and losses	203	580
Unrealized foreign currency translation adjustments	(3)	14
Unrecognized pension and other postretirement benefit cost arising during the period	0	(5)
Less: reclassification adjustment of net periodic cost recognized in operating costs and expenses	(19)	(16)
Unrecognized pension and other postretirement benefit cost	19	11
Other comprehensive income, after-tax	$ 219	$ 605