Investments - Realized Investment Gains and Losses (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Realized Gains (Losses) on Investments [Line Items]
Realized investment gains (losses) before income taxes	$ 169	$ 57	$ 154
Less income taxes (benefits)	60	17	48
Net realized investment gains (losses)	109	40	106
Fixed Maturities [Member]
Realized Gains (Losses) on Investments [Line Items]
Realized investment gains (losses) before income taxes	23	(82)	14
Equity securities [Member]
Realized Gains (Losses) on Investments [Line Items]
Realized investment gains (losses) before income taxes	(1)	36	13
Commercial Mortgage Loans [Member]
Realized Gains (Losses) on Investments [Line Items]
Realized investment gains (losses) before income taxes	4	(2)	(6)
Other Investments Including Derivatives [Member]
Realized Gains (Losses) on Investments [Line Items]
Realized investment gains (losses) before income taxes	$ 143	$ 105	$ 133