Fair Value Measurements (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Feb. 29, 2012	Feb. 29, 2012 Estimate of Fair Value, Fair Value Disclosure [Member]	Aug. 31, 2011 Estimate of Fair Value, Fair Value Disclosure [Member]	Feb. 28, 2011 Estimate of Fair Value, Fair Value Disclosure [Member]	Feb. 29, 2012 Fair Value, Inputs, Level 1 [Member]	Aug. 31, 2011 Fair Value, Inputs, Level 1 [Member]	Feb. 28, 2011 Fair Value, Inputs, Level 1 [Member]	Feb. 29, 2012 Fair Value, Inputs, Level 2 [Member]	Aug. 31, 2011 Fair Value, Inputs, Level 2 [Member]	Feb. 28, 2011 Fair Value, Inputs, Level 2 [Member]	Feb. 29, 2012 Fair Value, Inputs, Level 3 [Member]	Aug. 31, 2011 Fair Value, Inputs, Level 3 [Member]	Feb. 28, 2011 Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Money market funds		$ 764	$ 1,239	$ 1,138	$ 764	$ 1,239	$ 1,138	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0
Interest rate swaps		$ 55	$ 63	$ 38	$ 0	$ 0	$ 0	$ 55	$ 63	$ 38	$ 0	$ 0	$ 0
Interest rate swap valuation method	Interest rate swaps are valued using six-month LIBOR in arrears rates.