Other Comprehensive Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Pre-tax
Unrealized net holding gains and losses arising during the period, net of related offsets	$ 486	$ (1,896)	$ 1,026
Less: reclassification adjustment of realized capital gains and losses	(180)	112	597
Unrealized net capital gains and losses	666	(2,008)	429
Unrealized foreign currency translation adjustments	15	(89)	(62)
Unrecognized pension and other postretirement benefit cost arising during the period	(263)	(64)	(1,197)
Less: reclassification adjustment of net periodic cost recognized in operating costs and expenses	(100)	(134)	(78)
Unrecognized pension and other postretirement benefit cost	(163)	70	(1,119)
Other comprehensive income (loss)	518	(2,027)	(752)
Tax
Unrealized net holding gains and losses arising during the period, net of related offsets	(170)	663	(358)
Less: reclassification adjustment of realized capital gains and losses	63	(39)	(209)
Unrealized net capital gains and losses	(233)	702	(149)
Unrealized foreign currency translation adjustments	(5)	31	22
Unrecognized pension and other postretirement benefit cost arising during the period	94	25	421
Less: reclassification adjustment of net periodic cost recognized in operating costs and expenses	35	47	27
Unrecognized pension and other postretirement benefit cost	59	(22)	394
Other comprehensive income (loss)	(179)	711	267
After-tax
Unrealized net holding gains and losses arising during the period, net of related offsets	316	(1,233)	668
Less: reclassification adjustment of realized capital gains and losses	(117)	73	388
Unrealized net capital gains and losses	433	(1,306)	280
Unrealized foreign currency translation adjustments	10	(58)	(40)
Unrecognized pension and other postretirement benefit cost arising during the period	(169)	(39)	(776)
Less: reclassification adjustment of net periodic cost recognized in operating costs and expenses	(65)	(87)	(51)
Unrecognized pension and other postretirement benefit cost	(104)	48	(725)
Other comprehensive income (loss), after-tax	$ 339	$ (1,316)	$ (485)