Investments (Components of other-than-temporary impairment losses recognized in earnings) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Other-than-temporary impairment losses recognized in earnings	$ 81	$ 156	$ 77
Corporate and other bonds [Member]
Other-than-temporary impairment losses recognized in earnings	59	104	18
States, municipalities and political subdivisions [Member]
Other-than-temporary impairment losses recognized in earnings	0	18	46
Residential mortgage-backed [Member]
Other-than-temporary impairment losses recognized in earnings	10	8	5
Other asset-backed [Member]
Other-than-temporary impairment losses recognized in earnings	3	1	1
Total asset-backed [Member]
Other-than-temporary impairment losses recognized in earnings	13	9	6
Total fixed maturity securities available-for-sale [Member]
Other-than-temporary impairment losses recognized in earnings	72	131	70
Common stock [Member]
Other-than-temporary impairment losses recognized in earnings	$ 9	$ 25	$ 7