Share-based Compensation - Summary of Option Activity (Detail) $ / shares in Units, $ in Millions	12 Months Ended
	Sep. 30, 2019 USD ($) $ / shares shares
Aggregate Intrinsic Value
Stock price used to calculate aggregate intrinsic value (in dollars per share)	$ 172.01
Employee Stock Option
Options
Beginning balance (in shares) | shares	5,788,840
Granted (in shares) | shares	1,109,645
Forfeited (in shares) | shares	(108,973)
Expired (in shares) | shares	(33,574)
Exercised (in shares) | shares	(1,041,280)
Ending balance (in shares) | shares	5,714,658
Options exercisable at September 30, 2019 (in shares) | shares	3,230,165
Options exercisable and expected to vest at September 30, 2019 (in shares) | shares	5,635,182
Weighted- Average Exercise Price Per Share
Beginning balance (in dollars per share)	$ 75.30
Granted (in dollars per share)	134.76
Forfeited (in dollars per share)	114.04
Expired (in dollars per share)	28.85
Exercised (in dollars per share)	54.44
Ending balance (in dollars per share)	90.18
Options exercisable at September 30, 2019 (in dollars per share)	70.66
Options exercisable and expected to vest at September 30, 2019 (in dollars per share)	$ 89.69
Weighted- Average Remaining Contractual Term (in years)
Outstanding at September 30, 2019	6 years 9 months 29 days
Options exercisable at September 30, 2019	5 years 7 months 17 days
Options exercisable and expected to vest at September 30, 2019	6 years 9 months 18 days
Aggregate Intrinsic Value
Outstanding at September 30, 2019 | $	$ 468
Options exercisable at September 30, 2019 | $	327
Options exercisable and expected to vest at September 30, 2019 | $	$ 464