Investments - Scheduled Maturities (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Amortized cost
Due in one year or less	$ 1,337
Due after one year through five years	8,596
Due after five years through ten years	7,068
Due after ten years	3,990
Subtotal	20,991
ABS, RMBS and CMBS	654
Amortized cost	21,645	$ 22,004
Fair value
Due in one year or less	1,338
Due after one year through five years	8,781
Due after five years through ten years	7,089
Due after ten years	4,487
Subtotal	21,695
ABS, RMBS and CMBS	706
Fair value	$ 22,401	$ 23,261