Investments - Scheduled maturities for fixed income securities (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Amortized cost
Due in one year or less	$ 4,629
Due after one year through five years	28,201
Due after five years through ten years	16,363
Due after ten years	5,272
Subtotal	54,465
ABS, RMBS and CMBS	1,744
Amortized cost	56,209	$ 57,525
Fair value
Due in one year or less	4,627
Due after one year through five years	28,199
Due after five years through ten years	16,220
Due after ten years	5,782
Subtotal	54,828
ABS, RMBS and CMBS	1,846
Total fixed income securities	$ 56,674	$ 58,992