Investments - Realized Capital Gains and Losses (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Realized capital gains and losses by asset type
Realized capital gains and losses	$ (32)	$ (1)
Fixed income securities
Realized capital gains and losses by asset type
Realized capital gains and losses	(6)	(7)
Equity securities
Realized capital gains and losses by asset type
Realized capital gains and losses	(26)	0
Limited partnership interests
Realized capital gains and losses by asset type
Realized capital gains and losses	3	13
Derivatives
Realized capital gains and losses by asset type
Realized capital gains and losses	(3)	(5)
Other
Realized capital gains and losses by asset type
Realized capital gains and losses	$ 0	$ (2)