Investments - Fixed Maturities by Contractual Maturity Periods (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Amortized Cost:
Due in one year or less	$ 1,650
Due after one year through five years	6,364
Due after five years through ten years	10,363
Due after ten years	3,960
Mortgage and other asset-backed securities	532
Amortized Cost	22,869	$ 21,867
Fair Value:
Due in one year or less	1,656
Due after one year through five years	6,446
Due after five years through ten years	10,154
Due after ten years	4,474
Mortgage and other asset-backed securities	538
Total fair value	$ 23,268