Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Pre- tax
Other comprehensive (loss) income	$ (217)	$ 96
Tax
Other comprehensive (loss) income	46	(34)
After- tax
Other comprehensive (loss) income, after-tax	(171)	62
Accumulated Net Investment Gain (Loss)
Pre- tax
Unrealized net holding gains and losses arising during the period, net of related offsets	(224)	105
Less: reclassification adjustment of realized capital gains and losses	(2)	4
Other comprehensive (loss) income	(222)	101
Tax
Unrealized net holding gains and losses arising during the period, net of related offsets	47	(37)
Less: reclassification adjustment of realized capital gains and losses	0	(1)
Other comprehensive (loss) income	47	(36)
After- tax
Unrealized net holding gains and losses arising during the period, net of related offsets	(177)	68
Less: reclassification adjustment of realized capital gains and losses	(2)	3
Other comprehensive (loss) income, after-tax	(175)	65
Accumulated Foreign Currency Adjustment
Pre- tax
Other comprehensive (loss) income	5	(5)
Tax
Other comprehensive (loss) income	(1)	2
After- tax
Other comprehensive (loss) income, after-tax	$ 4	$ (3)