Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Pre- tax
Unrealized net holding gains and losses arising during the period, net of related offsets	$ 178	$ 351	$ 281	$ 674
Less: reclassification adjustment of realized capital gains and losses	(3)	(8)	(1)	(55)
Unrealized net capital gains and losses	181	359	282	729
Unrealized foreign currency translation adjustments	0	9	(5)	6
Other comprehensive income	181	368	277	735
Tax
Unrealized net holding gains and losses arising during the period, net of related offsets	(62)	(123)	(99)	(236)
Less: reclassification adjustment of realized capital gains and losses	1	3	0	19
Unrealized net capital gains and losses	(63)	(126)	(99)	(255)
Unrealized foreign currency translation adjustments	0	(3)	2	(2)
Other comprehensive income	(63)	(129)	(97)	(257)
After- tax
Unrealized net holding gains and losses arising during the period, net of related offsets	116	228	182	438
Less: reclassification adjustment of realized capital gains and losses	(2)	(5)	(1)	(36)
Unrealized net capital gains and losses	118	233	183	474
Unrealized foreign currency translation adjustments	0	6	(3)	4
Other comprehensive income, after-tax	$ 118	$ 239	$ 180	$ 478