Investments - Gross realized gains and losses on available for sale fixed maturity and equity security investment transactions (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Fixed maturities
Gross realized gains and losses on the sale of available for sale fixed maturity and equity security investments
Gross gains	$ 21	$ 33
Gross losses	(2)	(6)
Equity securities
Gross realized gains and losses on the sale of available for sale fixed maturity and equity security investments
Gross gains	15	36
Gross losses	$ (5)	$ (3)