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	$ 3,954	$ 3,861	$ 3,525
Acquisition costs deferred	5,001	4,717	4,596
Amortization charged to income	(4,784)	(4,550)	(4,364)
Effect of unrealized gains and losses	(46)	(74)	104
Balance, end of year	4,191	3,954	3,861
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
SquareTrade
Deferred policy acquisition costs
Acquisition costs deferred	$ 66	$ 0	$ 0