Income Taxes (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		12 Months Ended
	Jun. 30, 2020	Dec. 31, 2017	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Income Taxes [Line Items]
U.S. federal statutory tax rate		35.00%	21.00%	21.00%	24.50%
Discrete net tax expense related to Tax Act				$ 43.8	$ 180.6
Reversal of non-recurring benefit related to U.S. taxation of deemed foreign dividends				56.2
Tax benefit related to finalization of assessment of impacts of Tax Act				12.4
Reduction in equity affiliate income for impacts of the Tax Act					28.5
Provisional tax expense for deemed repatriation tax and additional foreign taxes on repatriation of earnings					392.4
Provisional tax expense for deemed repatriation tax					322.1
Provisional tax expense for additional foreign taxes on repatriation of earnings					70.3
Provisional tax benefit for re-measurement of net U.S. deferred tax liabilities at lower corporate tax rate					211.8
Deemed repatriation tax obligation after application of foreign tax credits			$ 211.4
Deemed repatriation tax obligation in noncurrent liabilities			$ 190.9	215.4
Period of payment on deemed repatriation tax obligation (in years)			6 years
Cash paid for taxes (net of cash refunds)			$ 379.9	324.3	372.0
Impact of tax holidays			$ 26.9
Impact of tax holidays (in dollars per share)			$ 0.12
Income tax provision related to estimated withholding taxes on future dividends	$ 20.3		$ 20.3
Proportionate share of accumulated dividend distribution taxes released per the India Finance Act	$ 33.8		33.8
Excess tax benefits from share-based compensation			20.0	14.6	21.5
Tax benefit from restructuring of foreign subsidiaries					35.7
Deferred tax assets, valuation allowance			95.0	92.1
Tax expense for deemed repatriation tax			373.2
Previously undistributed earnings of foreign subsidiaries and corporate joint ventures			5,800.0
Cumulative undistributed earnings			4,700.0
U.S. Income and foreign withholding taxes estimate			454.4
Unrecognized tax benefits			237.0	231.7	233.6	$ 146.4
Unrecognized tax benefits that would impact effective tax rate			86.1	75.0
Interest and penalties related to unrecognized tax benefits			6.1	12.0	(2.4)
Accrued interest and penalties			25.2	19.5
Additions for tax positions of prior years			17.7	14.2	119.2
Additions for tax positions of the current year			7.6	$ 7.8	26.4
Final audit settlement related to unrecognized tax benefits					43.1
Foreign Loss Carryforwards
Income Taxes [Line Items]
Deferred tax assets, valuation allowance			40.3
Foreign Capital Losses
Income Taxes [Line Items]
Deferred tax assets, valuation allowance			52.2
Discontinued Operations
Income Taxes [Line Items]
Tax benefit related to settlement and release of reserves					25.6
Continuing Operations
Income Taxes [Line Items]
Tax benefit related to settlement and release of reserves					$ 9.1
U.S. Federal
Income Taxes [Line Items]
Tax credit carryforwards			14.1
Increase in capital loss carryforwards			22.6
Foreign
Income Taxes [Line Items]
Tax credit carryforwards			28.6
Indefinite tax credit carryforwards			13.3
Operating loss carryforwards			236.6
Operating loss carryforwards not subject to expiration			83.1
Decrease in operating loss carryforwards			$ 116.0