Income Taxes (Narrative) (Details) - USD ($) $ in Millions		3 Months Ended				6 Months Ended		12 Months Ended
	Apr. 17, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Tax Disclosure [Line Items]
Deferred Foreign Income Tax Expense (Benefit)			$ 38.8
U.S. federal statutory tax rate (percent)			21.00%	35.00%
Net expense in consolidated income statements related to change in tax law						$ 239.0
Expense related to repatriation tax and future repatriation effect on foreign investments						453.0
Expense related to repatriation tax and future repatriation effect on foreign investments impacting income tax provision						420.5
Change In tax rate, deferred tax liability, income tax (expense) benefit						214.0
Component of tax-related adjustment payable over eight years						364.1
Component of tax-related adjustment resulting from withholding taxes and other impacts						56.4
Foreign tax credits expected to offset repatriation tax			$ 53.8			53.8
Tax liabilities not expected to be offset by foreign tax credits			310.3			310.3
Transition tax for accumulated foreign earnings, liability, noncurrent			263.4			$ 263.4
Effective tax rate (percent)						37.20%
Income tax payments, net of refunds						$ 153.7	$ 784.7
Unrecognized tax benefits			156.9			156.9			$ 146.4
Increase in unrecognized tax benefits resulting from current period tax positions						18.7
Decrease in unrecognized tax benefits resulting from prior period tax positions						9.7
Subsequent Event
Income Tax Disclosure [Line Items]
Decrease in unrecognized tax benefits resulting from settlement agreement	$ 40.0
Forecast
Income Tax Disclosure [Line Items]
U.S. federal statutory tax rate (percent)								24.50%
Forecast | Discontinued Operations
Income Tax Disclosure [Line Items]
Expected income tax benefit		$ 25.0
Forecast | Continuing Operations
Income Tax Disclosure [Line Items]
Expected income tax benefit		$ 9.0
Segment Reconciling Items
Income Tax Disclosure [Line Items]
Impact of new tax law on equity affiliate expense			$ 0.0		$ 0.0	$ 32.5	$ 0.0