Investments (Amortized Cost and Fair Value of Held-To-Maturity Debt Securities by Contractual Maturity) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011
Schedule of Held-to-maturity Securities [Line Items]
Due in one year or less, Amortized Cost	$ 43
Due after one year through five years, Amortized Cost	124
Due after five years through ten years, Amortized Cost	21
Due after ten years, Amortized Cost	9
Total debt securities - held-to-maturity, Amortized Cost	197
Due in one year or less, Fair Value	43
Due after one year through five years, Fair Value	127
Due after five years through ten years, Fair Value	22
Due after ten years, Fair Value	12
Total debt securities - held-to-maturity, Fair Value	$ 204