Investments - Realized capital gains and losses (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Realized capital gains and losses by asset type
Realized capital gains (losses)	$ (175)	$ 49	$ (77)
Fixed income securities
Realized capital gains and losses by asset type
Realized capital gains (losses)	(40)	(6)	(59)
Mortgage loans
Realized capital gains and losses by asset type
Realized capital gains (losses)	2	1	0
Equity securities
Realized capital gains and losses by asset type
Realized capital gains (losses)	(124)	21	(22)
Limited partnership interests
Realized capital gains and losses by asset type
Realized capital gains (losses)	(22)	46	(5)
Derivatives
Realized capital gains and losses by asset type
Realized capital gains (losses)	10	(16)	8
Other
Realized capital gains and losses by asset type
Realized capital gains (losses)	$ (1)	$ 3	$ 1