Short-Term Investments (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014
Short-term Investments [Abstract]
Available-for-sale securities,due in one year or less, fair value	$ 198
Held-to-maturity securities, due in one year or less, fair value	479
Available-for-sale securities, due after one year through three years, fair value	900
Held-to-maturity securities, due after one year through three years, fair value	0
Available-for-sale securities, due after three years through five years, fair value	199
Held-to-maturity securities, due after three years through five years, fair value	0
Available-for-sale securities, due after five years, fair value	76
Held-to-maturity securities, due after five years, fair value	0
Available-for-sale securities, total	1,373
Held-to-maturity securities, total	$ 479