Investments - Scheduled Maturities (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Amortized cost
Due in one year or less	$ 1,170
Due after one year through five years	8,135
Due after five years through ten years	7,149
Due after ten years	3,974
Subtotal	20,428
ABS, RMBS and CMBS	613
Amortized cost	21,041	$ 22,004
Fair value
Due in one year or less	1,177
Due after one year through five years	8,264
Due after five years through ten years	7,092
Due after ten years	4,370
Subtotal	20,903
ABS, RMBS and CMBS	664
Fair value	$ 21,567	$ 23,261