Investments - Scheduled maturities for fixed Income securities (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Amortized cost
Due in one year or less	$ 4,771
Due after one year through five years	28,736
Due after five years through ten years	16,956
Due after ten years	5,192
Subtotal	55,655
ABS, RMBS and CMBS	1,870
Amortized cost	57,525	$ 56,576
Fair value
Due in one year or less	4,783
Due after one year through five years	29,080
Due after five years through ten years	17,278
Due after ten years	5,873
Subtotal	57,014
ABS, RMBS and CMBS	1,978
Fair value	$ 58,992	$ 57,839