Investments - Realized Investment Gains and Losses (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Realized Gains (Losses) on Investments [Line Items]
Realized investment gains (losses) before income taxes	$ 46	$ (32)
Less income taxes (benefits)	15	(11)
Net realized investment gains (losses)	31	(21)
Fixed Maturities [Member]
Realized Gains (Losses) on Investments [Line Items]
Realized investment gains (losses) before income taxes	2	(18)
Equity securities [Member]
Realized Gains (Losses) on Investments [Line Items]
Realized investment gains (losses) before income taxes	33	(10)
Other Investments Including Derivatives [Member]
Realized Gains (Losses) on Investments [Line Items]
Realized investment gains (losses) before income taxes	$ 11	$ (4)