Debt - Additional Information (Detail) (USD $)			12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014 Syndicated Credit Facility [Member]	Sep. 30, 2014 Domestic Debt [Member] Syndicated Credit Facility [Member]
Debt Instrument [Line Items]
Short-term Debt, Weighted Average Interest Rate	0.40%	0.51%
Maximum borrowing capacity of syndicated credit facility				$ 1,000,000,000
Additional commitments made by the lenders				500,000,000
Maximum aggregate commitment	1,500,000,000
Borrowings under credit facility			0
Original expiration date of credit facility			May 31, 2017
Extended expiration date of credit facility			May 31, 2018
Credit facility, covenant description			The credit facility includes a single financial covenant that requires the Company to maintain an interest expense coverage ratio (ratio of earnings before income taxes, depreciation and amortization to interest expense) of not less than 5-to-1 for the most recent four consecutive fiscal quarters.
Credit facility, covenant compliance description			The Company was in compliance with this covenant as of September 30, 2014.
Aggregate annual maturities of long-term debt, 2015	0
Aggregate annual maturities of long-term debt, 2016	0
Aggregate annual maturities of long-term debt, 2017	500,000,000
Aggregate annual maturities of long-term debt, 2018	200,000,000
Aggregate annual maturities of long-term debt, 2019	$ 500,000,000