Investments - Gross realized gains and losses on available for sale fixed maturity investment transactions (Details) - Fixed maturities - USD ($) $ in Millions	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017
Gross realized gains and losses on the sale of available for sale fixed maturity and equity security investments
Gross gains	$ 19	$ 32
Gross losses	$ (8)	$ (4)

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