Investments (Details 2) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Amortized cost
Due in one year or less	$ 3,149
Due after one year through five years	24,722
Due after five years through ten years	23,511
Due after ten years	11,966
Subtotal	63,348
ABS, RMBS and CMBS	7,609
Total amortized cost for fixed income securities	70,957
Fair value
Due in one year or less	3,187
Due after one year through five years	25,905
Due after five years through ten years	25,450
Due after ten years	13,536
Subtotal	68,078
ABS, RMBS and CMBS	7,728
Total fixed income securities	$ 75,806	$ 77,017