Investments (Contractual maturity) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Investments [Abstract]
Due in one year or less, cost or amortized cost	$ 2,420	$ 1,648
Due after one year through five years, cost or amortized cost	9,496	13,603
Due after five years through ten years, cost or amortized cost	11,667	8,726
Due after ten years, cost or amortized cost	15,692	14,164
Total Amortized Cost Basis	39,275	38,141
Due in one year or less, estimated fair value	2,455	1,665
Due after one year through five years, estimated fair value	10,068	14,442
Due after five years through ten years, estimated fair value	11,954	9,555
Due after ten years, estimated fair value	16,720	16,942
Total Estimated Fair Value	$ 41,197	$ 42,604