New Accounting Guidance (Narrative) (Details) - USD ($) $ in Millions	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Equity	$ 14,088.0	$ 12,443.1	$ 11,388.3	$ 11,176.3
Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Equity	15,678.3	$ 14,875.7	$ 14,138.4	13,409.9
Cumulative-effect adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Equity				(17.1)
Cumulative-effect adjustment | Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Equity	$ 1.3			$ (17.1)