Share-Based Compensation - Summary of Stock Option Activity (Details) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Sep. 30, 2018 USD ($) $ / shares shares
Shares (in thousands)
Outstanding shares, beginning balance (in shares) | shares	3,889
Granted (in shares) | shares	894
Exercised (in shares) | shares	(798)
Forfeited (in shares) | shares	(68)
Canceled (in shares) | shares	(3)
Outstanding shares, ending balance (in shares) | shares	3,914
Shares (in thousands)
Vested or expected to vest (in shares) | shares	2,796
Exercisable (in shares) | shares	2,053
Wtd. Avg. Exercise Price
Outstanding, beginning balance (in dollars per share) | $ / shares	$ 108.10
Granted (in dollars per share) | $ / shares	191.87
Exercised (in dollars per share) | $ / shares	102.54
Forfeited (in dollars per share) | $ / shares	158.18
Canceled (in dollars per share) | $ / shares	94.85
Outstanding, ending balance (in dollars per share) | $ / shares	127.50
Vested or expected to vest (in dollars per share) | $ / shares	100.84
Exercisable (in dollars per share) | $ / shares	$ 101.20
Wtd. Avg. Remaining Contractual Terms (years) / Aggregate Intrinsic Value of In-The-Money Options
Outstanding, wtd. avg. remaining contractual term	6 years 11 months
Vested or expected to vest, wtd. avg. remaining contractual term	5 years 7 months
Exercisable, wtd. avg. remaining contractual term	5 years 6 months
Outstanding, Aggregate intrinsic value of in-the-money options | $	$ 234.9
Vested or expected, Aggregate intrinsic value of in-the-money options | $	242.4
Exercisable, Aggregate intrinsic value of in-the-money options | $	$ 177.2