Investment Income and Gains and Losses - Realized Investment Gains and Losses (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Realized Gains (Losses) on Investments [Line Items]
Realized investment gains (losses) before income taxes	$ 57	$ 154	$ 213
Less income taxes (benefits)	17	48	72
Net realized investment gains (losses)	40	106	141
Fixed Maturities [Member]
Realized Gains (Losses) on Investments [Line Items]
Realized investment gains (losses) before income taxes	(82)	14	113
Equity securities [Member]
Realized Gains (Losses) on Investments [Line Items]
Realized investment gains (losses) before income taxes	36	13	8
Commercial Mortgage Loans [Member]
Realized Gains (Losses) on Investments [Line Items]
Realized investment gains (losses) before income taxes	(2)	(6)	(3)
Other Investments Including Derivatives [Member]
Realized Gains (Losses) on Investments [Line Items]
Realized investment gains (losses) before income taxes	$ 105	$ 133	$ 95