Summary of Performance-based Shares Activity (Detail)	12 Months Ended
	Sep. 30, 2017 $ / shares shares
Aggregate Intrinsic Value
Stock price used to calculate aggregate intrinsic value	$ 105.24
Performance Awards
Shares
Beginning balance | shares	1,042,012
Granted | shares	634,651	[1]
Vested | shares	(345,797)
Unearned | shares	(97,531)
Forfeited | shares	(295,660)
Ending balance | shares	937,675
Weighted- Average Grant Date Fair Value
Beginning balance	$ 78.24
Granted	86.37	[1]
Vested	72.50
Unearned	72.50
Forfeited	85.13
Ending balance	$ 84.20
Weighted- Average Remaining Contractual Term
Outstanding at September 30, 2017	1 year
Aggregate Intrinsic Value
Outstanding at September 30, 2017	$ 98,000,000	[2]

[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 2017 of $105.24 by the number of instruments.