Investments - Maturities of Available for Sale and Held to Maturity Securities (Details) (USD $) In Millions, unless otherwise specified	Aug. 31, 2014
Available-For-Sale, Cost Basis
Due in one year or less	$ 148
Due after one year through five years	1,226
Due after five years	34
Available-For-Sale, Cost Basis, Total	1,408
Available-For-Sale, Fair Value
Due in one year or less	148
Due after one year through five years	1,227
Due after five years	34
Available-for-sale, Recorded Basis, Total	1,409
Held-To-Maturity
Due in one year or less	168
Due after one year through five years	0
Due after five years	0
Held-To-Maturity, Cost Basis, Total	$ 168