New Accounting Guidance (Narrative) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019
New Accounting Pronouncements [Line Items]
Equity	$ 13,134.8	$ 13,071.9	$ 12,443.1	$ 11,723.7	$ 11,929.8	$ 11,388.3
Retained Earnings
New Accounting Pronouncements [Line Items]
Equity	$ 15,200.0	$ 15,060.5	14,875.7	$ 14,537.2	$ 14,356.9	$ 14,138.4
Cumulative-effect adjustment | Retained Earnings
New Accounting Pronouncements [Line Items]
Equity			$ 1.3