Summary of RSA and RSU Activity (Detail) - $ / shares	12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Weighted-Average Remaining Contactual Term
Outstanding at September 30, 2016	5 years 2 months 19 days
Aggregate Intrinsic Value
Stock price used to calculate aggregate intrinsic value	$ 82.7
Restricted Stock Awards
Restricted stock
Beginning balance	4,064,687
Granted	0
Vested	(2,061,406)
Forfeited	(236,699)
Ending balance	1,766,582	4,064,687
Weighted-Average Grant Date Fair Value
Beginning balance	$ 54.09
Granted	0.00	$ 63.71	$ 49.98
Vested	49.06
Forfeited	59.34
Ending balance	$ 59.26	$ 54.09
Weighted-Average Remaining Contactual Term
Outstanding at September 30, 2016	10 months 6 days
Aggregate Intrinsic Value
Outstanding at September 30, 2016	$ 146,000,000
Restricted Stock Units
Restricted stock
Beginning balance	1,442,522
Granted	2,735,115
Vested	(789,180)
Forfeited	(241,503)
Ending balance	3,146,954	1,442,522
Weighted-Average Grant Date Fair Value
Beginning balance	$ 53.80
Granted	79.77	$ 62.88	$ 49.44
Vested	51.58
Forfeited	73.02
Ending balance	$ 75.48	$ 53.80
Weighted-Average Remaining Contactual Term
Outstanding at September 30, 2016	1 year 7 months 27 days
Aggregate Intrinsic Value
Outstanding at September 30, 2016	$ 260,000,000