Investment Income and Gains and Losses - Realized Investment Gains and Losses (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Realized Gains (Losses) on Investments [Line Items]
Realized investment gains (losses) before income taxes	$ 10	$ 23	$ 104	$ 130
Less income taxes (benefits)	3	8	36	45
Net realized investment gains (losses)	7	15	68	85
Fixed Maturities [Member]
Realized Gains (Losses) on Investments [Line Items]
Realized investment gains (losses) before income taxes	(57)	2	(38)	14
Equity securities [Member]
Realized Gains (Losses) on Investments [Line Items]
Realized investment gains (losses) before income taxes	28	(3)	42	14
Commercial Mortgage Loans [Member]
Realized Gains (Losses) on Investments [Line Items]
Realized investment gains (losses) before income taxes	0	(2)	2	(6)
Other Investments Including Derivatives [Member]
Realized Gains (Losses) on Investments [Line Items]
Realized investment gains (losses) before income taxes	$ 39	$ 26	$ 98	$ 108