Income Taxes (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		12 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Income Taxes [Line Items]
Cash paid for taxes (net of cash refunds)			$ 383.8	$ 379.9	$ 324.3
Cash provided by operating activities			$ 6.7	0.0	$ 0.0
Income tax provision related to estimated withholding taxes on future dividends				20.3
Proportionate share of accumulated dividend distribution taxes released per the India Finance Act				$ 33.8
U.S. federal statutory tax rate			21.00%	21.00%	21.00%
Discrete net tax expense related to Tax Act					$ 43.8
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
Deemed repatriation tax obligation after application of foreign tax credits	$ 177.7		$ 177.7
Deemed repatriation tax obligation in noncurrent liabilities	157.1		$ 157.1	$ 190.9
Period of payment on deemed repatriation tax obligation (in years)			5 years
Impact of tax holidays				$ 26.9
Impact of tax holidays (in dollars per share)				$ 0.12
Excess tax benefits from share-based compensation			$ 17.0	$ 20.0	14.6
Deferred tax assets, valuation allowance	97.6		97.6	95.0
Cumulative undistributed earnings	5,900.0		5,900.0
U.S. Income and foreign withholding taxes estimate	540.4		540.4
Unrecognized tax benefits that would impact effective tax rate	73.7		73.7
Reserves for unrecognized tax benefits decrease due to statute of limitations expiration			104.6	14.0	3.9
Interest and penalties related to unrecognized tax benefits			(0.2)	6.1	$ 12.0
Accrued interest and penalties	24.9		24.9	$ 25.2
Discontinued Operations
Income Taxes [Line Items]
Tax benefit related to release of reserves			60.0
Foreign Loss Carryforwards
Income Taxes [Line Items]
Deferred tax assets, valuation allowance	35.1		35.1
Foreign Capital Losses
Income Taxes [Line Items]
Deferred tax assets, valuation allowance	55.4		55.4
U.S. Federal
Income Taxes [Line Items]
Tax credit carryforwards	2.1		2.1
Foreign
Income Taxes [Line Items]
Tax credit carryforwards	27.5		27.5
Indefinite tax credit carryforwards	14.2		14.2
Operating loss carryforwards	258.8		258.8
Operating loss carryforwards not subject to expiration	111.5		111.5
PMD | Discontinued Operations
Income Taxes [Line Items]
Tax benefit related to release of reserves	$ 51.8		51.8
EfW | Discontinued Operations
Income Taxes [Line Items]
Tax benefit related to release of reserves		$ 8.2	8.2
Discontinued operations | PMD
Income Taxes [Line Items]
Reserves for unrecognized tax benefits decrease due to statute of limitations expiration			65.6
Related deferred tax assets			13.8
Discontinued operations | EfW
Income Taxes [Line Items]
Reserves for unrecognized tax benefits decrease due to statute of limitations expiration			8.2
Other reserves
Income Taxes [Line Items]
Reserves for unrecognized tax benefits decrease due to statute of limitations expiration			27.5
Related deferred tax assets			8.4
Tax benefit			$ 21.5