Investments - Fixed Maturities by Contractual Maturity Periods (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Amortized Cost:
Due in one year or less	$ 1,393
Due after one year through five years	6,822
Due after five years through ten years	8,905
Due after ten years	3,649
Mortgage and other asset-backed securities	453
Amortized Cost	21,222	$ 19,942
Fair Value:
Due in one year or less	1,407
Due after one year through five years	7,079
Due after five years through ten years	9,176
Due after ten years	4,368
Mortgage and other asset-backed securities	483
Total fair value	$ 22,513