Investments - Scheduled maturities (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Amortized cost
Due in one year or less	$ 1,392
Due after one year through five years	8,521
Due after five years through ten years	7,292
Due after ten years	4,118
Subtotal	21,323
ABS, RMBS and CMBS	681
Amortized cost	22,004	$ 23,112
Fair value
Due in one year or less	1,399
Due after one year through five years	8,845
Due after five years through ten years	7,524
Due after ten years	4,758
Subtotal	22,526
ABS, RMBS and CMBS	735
Total	$ 23,261	$ 24,222