Investments (Details 2) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Amortized cost
Amortized cost, fixed maturities	$ 9,499
Estimated fair value
Estimated fair value, fixed maturities	10,055	9,571
Indemnity
Amortized cost
Due in one year or less	71
Due after one year through five years	226
Due after five years through ten years	145
Due after ten years	103
Amortized cost, fixed maturities	545	555
Estimated fair value
Due in one year or less	71
Due after one year through five years	227
Due after five years through ten years	150
Due after ten years	108
Estimated fair value, fixed maturities	556	564
Exchange
Amortized cost
Due in one year or less	446
Due after one year through five years	3,320
Due after five years through ten years	3,656
Due after ten years	1,532
Amortized cost, fixed maturities	8,954	8,540
Estimated fair value
Due in one year or less	453
Due after one year through five years	3,512
Due after five years through ten years	3,852
Due after ten years	1,682
Estimated fair value, fixed maturities	$ 9,499	$ 9,007