Investments - Realized Investment Gains and Losses (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Realized Gains (Losses) on Investments [Line Items]
Realized investment gains (losses) before income taxes	$ 67	$ 21	$ 35	$ 94
Less income taxes (benefits)	23	8	12	33
Net realized investment gains (losses)	44	13	23	61
Fixed Maturities [Member]
Realized Gains (Losses) on Investments [Line Items]
Realized investment gains (losses) before income taxes	6	12	(12)	19
Equity securities [Member]
Realized Gains (Losses) on Investments [Line Items]
Realized investment gains (losses) before income taxes	11	1	1	14
Commercial Mortgage Loans [Member]
Realized Gains (Losses) on Investments [Line Items]
Realized investment gains (losses) before income taxes	4	(3)	4	2
Other Investments Including Derivatives [Member]
Realized Gains (Losses) on Investments [Line Items]
Realized investment gains (losses) before income taxes	$ 46	$ 11	$ 42	$ 59