Investments (Net investment income summary) (Details 2) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Investment income on fixed maturities	$ 1,349	$ 1,368	$ 1,403
Net realized gains	46	6	4
Affordable housing partnerships	(100)	(44)	(18)
Other	108	91	68
Consolidated investment entities	106	155	231
Total net investment income	$ 1,509	$ 1,576	$ 1,688