Reserve for Life-Contingent Contract Benefits and Contractholder Funds - Contractholder funds (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Contractholder funds activity
Balance, beginning of year	$ 18,592	$ 19,470	$ 20,542
Deposits	863	909	969
Interest credited	597	635	672
Benefits	(810)	(871)	(947)
Surrenders and partial withdrawals	(1,095)	(960)	(1,014)
Maturities of and interest payments on institutional products	0	0	(86)
Contract charges	(645)	(655)	(665)
Net transfers from separate accounts	7	4	5
Other adjustments	(39)	60	(6)
Balance, end of year	$ 17,470	$ 18,592	$ 19,470