Investments - Gross realized gains and losses on available for sale fixed maturity security investment transactions (Details) - Fixed maturities - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Gross realized gains and losses on the sale of available for sale fixed maturity security investments
Gross gains	$ 22	$ 43	$ 55
Gross losses	$ (14)	$ (20)	$ (10)

This item represents the gross profit realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

No definition available.

Name:	us-gaap_AvailableForSaleSecuritiesGrossRealizedGains
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration