Investments (Details 2) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Amortized cost
Total fixed maturities	$ 7,789
Estimated fair value
Total fixed maturities	8,163	8,159
Indemnity
Amortized cost
Due in one year or less	127
Due after one year through five years	198
Due after five years through ten years	34
Due after ten years	71
Total fixed maturities	430
Estimated fair value
Due in one year or less	127
Due after one year through five years	201
Due after five years through ten years	36
Due after ten years	74
Total fixed maturities	438	452
Exchange
Amortized cost
Due in one year or less	476
Due after one year through five years	2,730
Due after five years through ten years	2,655
Due after ten years	1,498
Total fixed maturities	7,359
Estimated fair value
Due in one year or less	486
Due after one year through five years	2,890
Due after five years through ten years	2,798
Due after ten years	1,551
Total fixed maturities	$ 7,725	$ 7,707