Deferred Policy Acquisition and Sales Inducement Costs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred policy acquisition costs
Balance, beginning of year	$ 1,187	$ 1,314	$ 1,271
Acquisition costs deferred	122	79	124
Amortization charged to income	(152)	(134)	(151)
Effect of unrealized gains and losses	(46)	(72)	99
Reinsurance ceded	45	0	(29)
Balance, end of year	1,156	1,187	1,314
DSI activity relates to fixed annuities and interest-sensitive life contracts
Balance, beginning of year	40	45	44
Sales inducements deferred	0	1	3
Amortization charged to income	(4)	(5)	(4)
Effect of unrealized gains and losses	0	(1)	2
Balance, end of year	$ 36	$ 40	$ 45