Investments - Gross realized gains and losses on available for sale fixed maturity investment transactions (Details) - Fixed maturities - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Gross realized gains and losses on the sale of available for sale fixed maturity and equity security investments
Gross gains	$ 6	$ 6
Gross losses	$ (9)	$ (3)

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