Investments - Realized Investment Gains and Losses (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Realized Gains (Losses) on Investments [Line Items]
Realized investment gains (losses) before income taxes	$ (32)	$ 73
Less income taxes (benefits)	(11)	25
Net realized investment gains (losses)	(21)	48
Fixed Maturities [Member]
Realized Gains (Losses) on Investments [Line Items]
Realized investment gains (losses) before income taxes	(18)	7
Equity securities [Member]
Realized Gains (Losses) on Investments [Line Items]
Realized investment gains (losses) before income taxes	(10)	13
Commercial Mortgage Loans [Member]
Realized Gains (Losses) on Investments [Line Items]
Realized investment gains (losses) before income taxes	0	5
Other Investments Including Derivatives [Member]
Realized Gains (Losses) on Investments [Line Items]
Realized investment gains (losses) before income taxes	$ (4)	$ 48