Investments - Net Realized Capital Gains (Losses) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Available-for-sale Securities Including Securities Pledged [Line Items]
Equity Securities, Securities Still Held, Change in Fair Value Recognized through the Income Statement	$ 2		$ 0
Realized capital gains (losses)	(83)	$ (47)	(170)	$ (103)
After-tax net realized capital gains (losses), after tax	(61)	(31)	(140)	(67)
Proceeds from sale of investments
Proceeds on sales	1,180	561	1,840	1,638
Gross gains	7	6	11	11
Gross losses	20	7	27	25
Derivatives
Available-for-sale Securities Including Securities Pledged [Line Items]
Realized capital gains (losses)	6	2	11	6
Other investments
Available-for-sale Securities Including Securities Pledged [Line Items]
Realized capital gains (losses)	0	0	5	0
Fixed Maturities, Available-for-sale, Including Securities Pledged
Available-for-sale Securities Including Securities Pledged [Line Items]
Realized capital gains (losses)	(19)	(1)	(33)	(21)
Fixed maturities, at fair value using the fair value option
Available-for-sale Securities Including Securities Pledged [Line Items]
Realized capital gains (losses)	(82)	(38)	(181)	(97)
Equity securities
Available-for-sale Securities Including Securities Pledged [Line Items]
Realized capital gains (losses)	2	0	0	0
Embedded derivatives - fixed maturities
Available-for-sale Securities Including Securities Pledged [Line Items]
Realized capital gains (losses)	(2)	(1)	(4)	(2)
Guaranteed benefit derivatives
Available-for-sale Securities Including Securities Pledged [Line Items]
Realized capital gains (losses)	$ 12	$ (9)	$ 32	$ 11