Investments (Details 5) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Net Investment Income [Line Items]
Gross investment income	$ 1,651	$ 1,513	$ 1,363
Investment expenses	(18)	(12)	(17)
Net investment income	1,633	1,501	1,346
Fixed maturities [Member]
Net Investment Income [Line Items]
Gross investment income	1,461	1,352	1,241
Equity securities [Member]
Net Investment Income [Line Items]
Gross investment income	76	66	50
Equity Method Investments [Member]
Net Investment Income [Line Items]
Gross investment income	27	18	0	[1]
Other [Member]
Net Investment Income [Line Items]
Gross investment income	$ 87	$ 77	$ 72

[1] Prior to 2014, equity in the earnings of partnerships was not material and was included in realized gains (losses) on securities.