Investments - Realized capital gains and losses by asset type (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	$ (134)	$ 134
Fixed income securities
Realized capital gains and losses by asset type
Realized capital gains and losses	(43)	5
Equity securities
Realized capital gains and losses by asset type
Realized capital gains and losses	(93)	106
Limited partnership interests
Realized capital gains and losses by asset type
Realized capital gains and losses	10	40
Derivatives
Realized capital gains and losses by asset type
Realized capital gains and losses	(8)	(15)
Other
Realized capital gains and losses by asset type
Realized capital gains and losses	$ 0	$ (2)