Investments (Details 2) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Amortized cost
Due in one year or less	$ 2,153
Due after one year through five years	8,812
Due after five years through ten years	15,751
Due after ten years	9,379
Subtotal	36,095
ABS, RMBS and CMBS	4,597
Total	40,692
Fair value
Due in one year or less	2,181
Due after one year through five years	9,476
Due after five years through ten years	17,158
Due after ten years	10,784
Subtotal	39,599
ABS, RMBS and CMBS	4,624
Total	$ 44,223	$ 44,876