Investments - Scheduled maturities for fixed income securities (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Amortized cost
Due in one year or less	$ 4,289
Due after one year through five years	28,481
Due after five years through ten years	15,933
Due after ten years	6,455
Subtotal	55,158
ABS, RMBS and CMBS	1,592
Amortized cost	56,750	$ 57,525
Fair value
Due in one year or less	4,293
Due after one year through five years	28,384
Due after five years through ten years	15,673
Due after ten years	6,848
Subtotal	55,198
ABS, RMBS and CMBS	1,693
Total fixed income securities	$ 56,891	$ 58,992