Income Taxes - Additional Information (Details) - USD ($) $ in Millions		3 Months Ended		12 Months Ended
	Dec. 22, 2017	Jun. 30, 2020	Dec. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Income Taxes [Line Items]
Statutory tax rate	21.00%
Tax cuts and jobs act, accounting complete			true
Income tax expense from revaluation of deferred tax assets and liabilities			$ 0.4
Additional income tax expense from transition tax provisional liability			$ 3.7
Decrease in transition tax reserve based on adjustments to expected post-1986 deferred foreign income		$ 16.4
Operating Loss Carryforwards				$ 2.6	$ 4.0
Deferred income tax assets:
Federal and foreign net operating loss carryforwards				188.3	173.5
Deferred income tax liabilities:
Operating Loss Carryforwards				2.6	4.0
Undistributed Foreign Earnings				1,700.0
Balance at end of fiscal year				206.7	224.3	$ 127.1	$ 148.9
Unrecognized Tax Benefits that Would Impact Effective Tax Rate				189.5	207.5
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued				72.4	80.0
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense				6.6	9.7	$ 5.8
Decrease in Unrecognized Tax Benefits is Reasonably Possible				21.9
State and Local Jurisdiction [Member]
Income Taxes [Line Items]
Operating Loss Carryforwards				1,795.0	1,638.0
Deferred income tax assets:
State net operating loss carryforwards				67.0	57.6
Tax Credit Carryforward, Deferred Tax Asset				79.4	69.5
Tax credit carryforward, valuation allowance				71.9	56.8
Deferred income tax liabilities:
Operating Loss Carryforwards				1,795.0	1,638.0
Operating Loss Carryforwards, Valuation Allowance				12.7	10.2
Foreign Country [Member]
Income Taxes [Line Items]
Operating Loss Carryforwards				765.1	663.2
Deferred income tax assets:
Federal and foreign net operating loss carryforwards				187.7	172.5
Deferred income tax liabilities:
Operating Loss Carryforwards				765.1	663.2
Operating Loss Carryforwards, Valuation Allowance				$ 165.9	$ 144.1
Minimum [Member]
Deferred income tax liabilities:
Operating loss carryforward expiration				Oct. 01, 2031
Minimum [Member] | State and Local Jurisdiction [Member]
Deferred income tax liabilities:
Operating loss carryforward expiration				Oct. 01, 2022
Tax Credit Carryforward, Years to Expiration				5 years
Minimum [Member] | Foreign Country [Member]
Deferred income tax liabilities:
Operating loss carryforward expiration				Oct. 01, 2022
Maximum [Member]
Deferred income tax liabilities:
Operating loss carryforward expiration				Sep. 30, 2038
Maximum [Member] | State and Local Jurisdiction [Member]
Deferred income tax liabilities:
Operating loss carryforward expiration				Sep. 30, 2040
Tax Credit Carryforward, Years to Expiration				10 years
Maximum [Member] | Foreign Country [Member]
Deferred income tax liabilities:
Operating loss carryforward expiration				Sep. 30, 2040