Reserves for Future Policy Benefits and Contract Owner Account Balances - Future Policy Benefits (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Liability for Future Policy Benefit, by Product Segment [Line Items]
Future policy benefits	$ 9,945	$ 9,587
Individual and group life insurance contracts
Liability for Future Policy Benefit, by Product Segment [Line Items]
Future policy benefits	2,982	3,341
Product guarantees on universal life and deferred annuity contracts, and payout contracts with life contingencies
Liability for Future Policy Benefit, by Product Segment [Line Items]
Future policy benefits	6,141	5,435
Accident and health
Liability for Future Policy Benefit, by Product Segment [Line Items]
Future policy benefits	$ 822	$ 811