Income Taxes - Reconciliation of U.S. Federal Statutory Tax Rate to Effective Tax Rate (Details)	12 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Operating Loss Carryforwards [Line Items]
U.S. federal statutory tax rate	21.00%	21.00%	24.50%
Difference in tax rate due to:
Noncontrolling interests not subject to tax	0.00%	(2.70%)	(3.00%)
State income taxes, net of federal benefit	2.80%	3.60%	2.90%
Valuation allowance adjustments	0.00%	0.00%	1.10%
Effects of foreign operations	1.30%	1.80%	3.10%
Excess tax benefits on share-based payments	(0.20%)	(1.00%)	(1.10%)
Other, net	(0.30%)	0.70%	(0.70%)
Effective tax rate	20.20%	23.10%	3.80%
Effect of U.S. tax legislation
Difference in tax rate due to:
Effect of tax rate change	(4.70%)	0.20%	(20.90%)
Effect of tax rate change	(4.70%)	0.20%	(20.90%)
Effect of tax rate changes - International
Difference in tax rate due to:
Effect of tax rate change	0.30%	(0.50%)	(2.10%)
Effect of tax rate change	0.30%	(0.50%)	(2.10%)

Difference in tax rate due to.

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Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to changes in the valuation allowance for deferred tax assets.

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations applicable to statutory income tax expense (benefit) outside of the country of domicile.

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to noncontrolling interest income (loss) exempt from income taxes.

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Percentage of difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying domestic federal statutory income tax rate to pretax income (loss) from continuing operation, attributable to expense for award under share-based payment arrangement. Excludes expense determined to be nondeductible upon grant or after for award under share-based payment arrangement.

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations applicable to state and local income tax expense (benefit), net of federal tax expense (benefit).

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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