Stock-Based Compensation - Stock Options (Details) $ / shares in Units, $ in Millions	12 Months Ended
	Sep. 30, 2023 USD ($) $ / shares shares
Weighted Average Option Price
Outstanding options, beginning period (in dollars per share) | $ / shares	$ 38.32
Options exercisable, beginning period (in dollars per share) | $ / shares	38.32
Exercised (in dollars per share) | $ / shares	25.79
Forfeited or expired (in dollars per share) | $ / shares	27.54
Outstanding options, ending period (in dollars per share) | $ / shares	48.93
Options exercisable, ending period (in dollars per share) | $ / shares	$ 48.93
Shares Subject to Option
Options outstanding at beginning period (in shares) | shares	49,939
Options exercisable, beginning period (in shares) | shares	49,939
Options exercised (in shares) | shares	(20,638)
Forfeited or expired (in shares) | shares	(2,444)
Options outstanding at ending period (in shares) | shares	26,857
Options exercisable, ending period (in shares) | shares	26,857
Weighted Average Remaining Contractual Life (years)
Options outstanding, weighted average remaining contractual life	1 year 3 months 18 days
Options exercisable, weighted average remaining contractual life	1 year 3 months 18 days
Aggregate Intrinsic Value (in millions)
Options outstanding, aggregate intrinsic value | $	$ 0
Options exercisable, aggregate intrinsic value | $	$ 0