Investments (Net change in unrealized gains (losses) on investments) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Net change in unrealized gains (losses) on investments	$ 224	$ (1,119)	$ 1,517
Fixed maturity securities [Member]
Net change in unrealized gains (losses) on investments	225	(1,114)	1,511
Total equity securities available-for-sale [Member]
Net change in unrealized gains (losses) on investments	(2)	(6)	6
Other [Member]
Net change in unrealized gains (losses) on investments	$ 1	$ 1	$ 0