Investments (Amortized Cost and Fair Value of Held-To-Maturity Debt Securities by Contractual Maturity) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Schedule of Held-to-maturity Securities [Line Items]
Due in one year or less, Amortized Cost	$ 88
Due after one year through five years, Amortized Cost	210
Due after five years through ten years, Amortized Cost	112
Due after ten years, Amortized Cost	85
Held-to-maturity securities, Amortized Cost	495	543
Due in one year or less, Fair Value	88
Due after one year through five years, Fair Value	210
Due after five years through ten years, Fair Value	113
Due after ten years, Fair Value	86
Total debt securities - held-to-maturity, Fair Value	$ 497	$ 544