Reserve for Life-Contingent Contract Benefits and Contractholder Funds - Liabilities for guarantees narrative (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Liabilities for guarantees:
Liability for guarantees	$ 443	$ 369	$ 364
Variable annuities | In the event of death
Liabilities for guarantees:
Liability for guarantees	109	85	100
Variable annuities | Liability for guarantees related to income benefits
Liabilities for guarantees:
Liability for guarantees	36	26	40
Variable annuities | Guaranteed accumulation benefits
Liabilities for guarantees:
Liability for guarantees	25	22	34
Variable annuities | For cumulative periodic withdrawals
Liabilities for guarantees:
Liability for guarantees	14	12	9
Variable annuities | Other guarantees
Liabilities for guarantees:
Liability for guarantees	$ 259	$ 224	$ 181