Investments - Realized Investment Gains and Losses (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Realized Gains (Losses) on Investments [Line Items]
Realized investment gains (losses) before income taxes	$ 75	$ 10	$ 110	$ 104
Less income taxes (benefits)	27	3	39	36
Net realized investment gains (losses)	48	7	71	68
Fixed Maturities [Member]
Realized Gains (Losses) on Investments [Line Items]
Realized investment gains (losses) before income taxes	7	(57)	(5)	(38)
Equity securities [Member]
Realized Gains (Losses) on Investments [Line Items]
Realized investment gains (losses) before income taxes	(1)	28	0	42
Commercial Mortgage Loans [Member]
Realized Gains (Losses) on Investments [Line Items]
Realized investment gains (losses) before income taxes	0	0	4	2
Other Investments Including Derivatives [Member]
Realized Gains (Losses) on Investments [Line Items]
Realized investment gains (losses) before income taxes	$ 69	$ 39	$ 111	$ 98