Investments - Fixed Maturities by Contractual Maturity Periods (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Amortized Cost:
Due in one year or less	$ 1,604
Due after one year through five years	6,798
Due after five years through ten years	10,455
Due after ten years	4,068
Mortgage and other asset-backed securities	491
Amortized Cost	23,416	$ 21,867
Fair Value:
Due in one year or less	1,614
Due after one year through five years	6,923
Due after five years through ten years	10,416
Due after ten years	4,716
Mortgage and other asset-backed securities	509
Total fair value	$ 24,178