Investments - Gross realized gains and losses on available for sale fixed maturity and equity security investment transactions (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Fixed maturities
Gross realized gains and losses on the sale of available for sale fixed maturity and equity security investments
Gross gains	$ 32	$ 44
Gross losses	(4)	(8)
Equity securities
Gross realized gains and losses on the sale of available for sale fixed maturity and equity security investments
Gross gains	36	49
Gross losses	$ (6)	$ (3)