Investments - Net Realized Capital Gains (Losses) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 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	$ (1)		$ (1)
Realized capital gains (losses)	(44)	$ (42)	(214)	$ (145)
After-tax net realized capital gains (losses), after tax	(41)	(28)	(181)	(94)
Proceeds from sale of investments
Proceeds on sales	120	551	1,960	2,189
Gross gains	1	6	12	17
Gross losses	4	6	31	31
Derivatives
Available-for-sale Securities Including Securities Pledged [Line Items]
Realized capital gains (losses)	23	4	34	11
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)	(9)	(2)	(42)	(23)
Fixed maturities, at fair value using the fair value option
Available-for-sale Securities Including Securities Pledged [Line Items]
Realized capital gains (losses)	(80)	(50)	(261)	(147)
Equity securities
Available-for-sale Securities Including Securities Pledged [Line Items]
Realized capital gains (losses)	(1)	0	(1)	0
Embedded derivatives - fixed maturities
Available-for-sale Securities Including Securities Pledged [Line Items]
Realized capital gains (losses)	(1)	(1)	(5)	(4)
Guaranteed benefit derivatives
Available-for-sale Securities Including Securities Pledged [Line Items]
Realized capital gains (losses)	$ 24	$ 7	$ 56	$ 18