Credit Arrangements (Long-term Debt, Including the Deferred Gain from the Termination of the Interest Rate Swaps) (Details) (USD $)	6 Months Ended	12 Months Ended
	Feb. 28, 2014	Aug. 31, 2013	May 31, 2013
Debt Instrument [Line Items]
Total long-term debt including current maturities	$ 1,283,535,000	$ 1,284,042,000
Current maturities of long-term debt	6,776,000	5,228,000
Long-term debt	1,276,759,000	1,278,814,000
$400 million notes at 6.50% due July 2017 [Member]
Debt Instrument [Line Items]
Debt instrument, face amount	400,000,000	400,000,000
Debt instrument, interest rate, stated percentage	6.50%	6.50%
Debt instrument, maturity date	July 2017	July 2017
Weighted average interest rate	5.70%
Total long-term debt including current maturities		411,518,000
$500 million notes at 7.35% due August 2018 [Member]
Debt Instrument [Line Items]
Debt instrument, face amount	500,000,000	500,000,000
Debt instrument, interest rate, stated percentage	7.35%	7.35%
Debt instrument, maturity date	August 2018	August 2018
Weighted average interest rate	6.40%
Total long-term debt including current maturities		522,930,000
$330 million notes at 4.875% due May 2023 [Member]
Debt Instrument [Line Items]
Debt instrument, face amount	330,000,000	330,000,000	330,000,000
Debt instrument, interest rate, stated percentage	4.875%	4.875%	4.875%
Debt instrument, maturity date	May 15, 2023	May 15, 2023
Weighted average interest rate	4.90%
Total long-term debt including current maturities		330,000,000
Other, including equipment notes [Member]
Debt Instrument [Line Items]
Total long-term debt including current maturities	$ 22,886,000	$ 19,594,000