Investments - Net Realized Capital Gains (Losses) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 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)
Realized capital gains (losses)	(87)	$ (55)
After-tax net realized capital gains (losses), after tax	(79)	(36)
Proceeds from sale of investments
Proceeds on sales	660	1,077
Gross gains	4	5
Gross losses	7	18
Derivatives
Available-for-sale Securities Including Securities Pledged [Line Items]
Realized capital gains (losses)	5	4
Other investments
Available-for-sale Securities Including Securities Pledged [Line Items]
Realized capital gains (losses)	5	0
Fixed Maturities, Available-for-sale, Including Securities Pledged
Available-for-sale Securities Including Securities Pledged [Line Items]
Realized capital gains (losses)	(14)	(19)
Fixed maturities, at fair value using the fair value option
Available-for-sale Securities Including Securities Pledged [Line Items]
Realized capital gains (losses)	(99)	(59)
Equity securities
Available-for-sale Securities Including Securities Pledged [Line Items]
Realized capital gains (losses)	(2)	0
Embedded derivatives - fixed maturities
Available-for-sale Securities Including Securities Pledged [Line Items]
Realized capital gains (losses)	(2)	(1)
Guaranteed benefit derivatives
Available-for-sale Securities Including Securities Pledged [Line Items]
Realized capital gains (losses)	$ 20	$ 20