Low Income Housing Partnerships (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Investments in Affordable Housing Projects [Abstract]
Investment In affordable housing limited partnerships	$ 101.2	$ 89.7
Obligations related to investments in affordable housing limited partnerships	$ 51.6	44.5
Affordable housing tax credits commitment, year to be paid	2023
Proportional amortization expense, amount	$ 8.4	7.9	$ 6.8
Affordable housing tax credits, amount	10.5	9.8	8.6
Net income tax benefit, low income housing partnerships	2.1	1.9	1.8
Impairment losses from the forfeiture or ineligibility of tax credits or other circumstances, amount	$ 0.0	$ 0.0	$ 0.0