Investments - Debt Maturities (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Fixed maturities
Available-for-sale Securities Including Securities Pledged [Line Items]
One year or less, Amortized Cost	$ 563
One year or less, Fair Value	568
After one year through five years, Amortized Cost	3,738
After one year through five years, Fair Value	3,845
After five years through ten years, Amortized Cost	5,758
After five years through ten years, Fair Value	5,911
After ten years, Amortized Cost	8,197
After ten years, Fair Value	8,851
Fixed maturities, including securities pledged, Amortized Cost	24,863	$ 24,898
Fixed maturities, including securities pledged, Fair Value	25,902	$ 25,034
Mortgage-backed securities
Available-for-sale Securities Including Securities Pledged [Line Items]
Without single maturity date, Amortized Cost	5,271
Without single maturity date, Fair Value	$ 5,398
Percentage collateralized of mortgage backed securities including interest-only strip or principal-only strip	50.80%	52.50%
Other asset-backed securities
Available-for-sale Securities Including Securities Pledged [Line Items]
Without single maturity date, Amortized Cost	$ 1,336
Without single maturity date, Fair Value	1,329
Fixed maturities, including securities pledged, Amortized Cost	1,336	$ 1,230
Fixed maturities, including securities pledged, Fair Value	$ 1,329	$ 1,208