Summary of Performance-based Shares Activity (Detail) - $ / shares		12 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Aggregate Intrinsic Value
Stock price used to calculate aggregate intrinsic value		$ 150.09
Performance Awards
Shares
Beginning balance		937,675
Granted	[1]	641,498
Vested		(355,563)
Unearned		(48,980)
Forfeited		(175,214)
Ending balance		999,416	937,675
Weighted- Average Grant Date Fair Value
Beginning balance		$ 84.20
Granted	[1]	120.11	$ 86.37	$ 92.71
Vested		88.05
Unearned		76.07
Forfeited		108.05
Ending balance		$ 102.07	$ 84.20
Weighted- Average Remaining Contractual Term
Outstanding at September 30, 2018		11 months 9 days
Aggregate Intrinsic Value
Outstanding at September 30, 2018	[2]	$ 150,000,000

[1] Represents the maximum number of performance-based shares which could be earned.

[2] Calculated by multiplying the closing stock price on the last trading day of fiscal 2018 of $150.09 by the number of instruments.