Investments (Details 2) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Amortized cost
Total fixed maturities	$ 8,032
Estimated fair value
Total fixed maturities	8,420	8,159
Indemnity
Amortized cost
Due in one year or less	106
Due after one year through five years	239
Due after five years through ten years	71
Due after ten years	75
Total fixed maturities	491
Estimated fair value
Due in one year or less	106
Due after one year through five years	242
Due after five years through ten years	73
Due after ten years	78
Total fixed maturities	499	452
Exchange
Amortized cost
Due in one year or less	476
Due after one year through five years	2,681
Due after five years through ten years	2,781
Due after ten years	1,603
Total fixed maturities	7,541
Estimated fair value
Due in one year or less	484
Due after one year through five years	2,862
Due after five years through ten years	2,927
Due after ten years	1,648
Total fixed maturities	$ 7,921	$ 7,707