Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Pre- tax
Unrealized net holding gains and losses arising during the period, net of related offsets	$ 90	$ 97	$ 366	$ 763
Less: reclassification adjustment of realized capital gains and losses	21	(15)	15	(78)
Unrealized net capital gains and losses	69	112	351	841
Unrealized foreign currency translation adjustments	13	(4)	8	2
Other comprehensive income	82	108	359	843
Tax
Unrealized net holding gains and losses arising during the period, net of related offsets	(31)	(34)	(128)	(267)
Less: reclassification adjustment of realized capital gains and losses	(7)	5	(5)	27
Unrealized net capital gains and losses	(24)	(39)	(123)	(294)
Unrealized foreign currency translation adjustments	(5)	1	(3)	(1)
Other comprehensive income	(29)	(38)	(126)	(295)
After- tax
Unrealized net holding gains and losses arising during the period, net of related offsets	59	63	238	496
Less: reclassification adjustment of realized capital gains and losses	14	(10)	10	(51)
Unrealized net capital gains and losses	45	73	228	547
Unrealized foreign currency translation adjustments	8	(3)	5	1
Other comprehensive income, after-tax	$ 53	$ 70	$ 233	$ 548