Other Comprehensive Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pre- tax
Other comprehensive income (loss)	$ 25	$ 240	$ (1,319)
Tax
Other comprehensive income (loss)	(9)	(83)	461
After- tax
Other comprehensive income (loss), after-tax	16	157	(858)
Accumulated Net Investment Gain (Loss)
Pre- tax
Unrealized net holding gains and losses arising during the period, net of related offsets	51	134	(1,048)
Less: reclassification adjustment of realized capital gains and losses	43	(100)	265
Other comprehensive income (loss)	8	234	(1,313)
Tax
Unrealized net holding gains and losses arising during the period, net of related offsets	(18)	(46)	366
Less: reclassification adjustment of realized capital gains and losses	(15)	35	(93)
Other comprehensive income (loss)	(3)	(81)	459
After- tax
Unrealized net holding gains and losses arising during the period, net of related offsets	33	88	(682)
Less: reclassification adjustment of realized capital gains and losses	28	(65)	172
Other comprehensive income (loss), after-tax	5	153	(854)
Accumulated Foreign Currency Adjustment
Pre- tax
Other comprehensive income (loss)	17	6	(6)
Tax
Other comprehensive income (loss)	(6)	(2)	2
After- tax
Other comprehensive income (loss), after-tax	$ 11	$ 4	$ (4)