Income Taxes (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2019	Mar. 31, 2018
Income Tax Disclosure [Abstract]
U.S. federal statutory tax rate (percent)	21.00%		35.00%
Discrete net tax expense related to Tax Act				$ 40.6
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				$ 15.6
Discrete net tax expense based on provisional estimates related to Tax Act					$ 206.5
Impact of new tax law on equity affiliate expense					$ 32.5
Deferred foreign income tax expense (benefit)		$ 38.8
Effective tax rate (percent)	19.90%	11.70%		23.30%	37.20%
Income tax payments, net of refunds				$ 165.6	$ 153.7