Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Pre-tax
Unrealized net holding gains and losses arising during the period, net of related offsets	$ 663	$ (1,003)	$ 1,381	$ (528)
Less: reclassification adjustment of realized capital gains and losses	11	100	(163)	251
Unrealized net capital gains and losses	652	(1,103)	1,544	(779)
Unrealized foreign currency translation adjustments	7	(13)	29	(55)
Unrecognized pension and other postretirement benefit cost arising during the period	1	(3)	(7)	8
Less: reclassification adjustment of net periodic cost recognized in operating costs and expenses	(24)	(33)	(48)	(65)
Unrecognized pension and other postretirement benefit cost	25	30	41	73
Other comprehensive income (loss)	684	(1,086)	1,614	(761)
Tax
Unrealized net holding gains and losses arising during the period, net of related offsets	(232)	350	(483)	184
Less: reclassification adjustment of realized capital gains and losses	(4)	(35)	57	(88)
Unrealized net capital gains and losses	(228)	385	(540)	272
Unrealized foreign currency translation adjustments	(2)	4	(10)	19
Unrecognized pension and other postretirement benefit cost arising during the period	0	2	3	(1)
Less: reclassification adjustment of net periodic cost recognized in operating costs and expenses	9	12	17	23
Unrecognized pension and other postretirement benefit cost	(9)	(10)	(14)	(24)
Other comprehensive income (loss), Tax	(239)	379	(564)	267
After-tax
Unrealized net holding gains and losses arising during the period, net of related offsets	431	(653)	898	(344)
Less: reclassification adjustment of realized capital gains and losses	7	65	(106)	163
Unrealized net capital gains and losses	424	(718)	1,004	(507)
Unrealized foreign currency translation adjustments	5	(9)	19	(36)
Unrecognized pension and other postretirement benefit cost arising during the period	1	(1)	(4)	7
Less: reclassification adjustment of net periodic cost recognized in operating costs and expenses	(15)	(21)	(31)	(42)
Unrecognized pension and other postretirement benefit cost	16	20	27	49
Other comprehensive income (loss), after-tax	$ 445	$ (707)	$ 1,050	$ (494)