Retirement and Postretirement Benefit Plans (Schedule of Postretirement Health Care Plan) (Details) - USD ($)	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Change in benefit obligation:
Benefit obligation at beginning of year	$ 371,800,000
Benefit obligation at end of year	363,800,000	$ 371,800,000
Amounts recorded in the Consolidated Balance Sheets:
Accrued benefits obligation, long-term	73.8	89,300,000
Postretirement Health Coverage [Member]
Change in benefit obligation:
Benefit obligation at beginning of year	12,200,000	12,700,000
Service cost	100,000	100,000
Interest cost	100,000	200,000
Actuarial loss (gain)	1,800,000	(400,000)
Defined Benefit Plan, Benefit Obligation, Benefits Paid	1,800,000	1,000,000.0
Defined Benefit Plan, Benefit Obligation, Contributions by Plan Participant	400,000	200,000
Benefit obligation at end of year	12,900,000	12,200,000
Amounts recorded in the Consolidated Balance Sheets:
Accrued benefits obligation, current portion	2,000,000.0	1,600,000
Accrued benefits obligation, long-term	10,900,000	10,600,000
Net amount recognized	12,900,000	12,200,000
Special Termination Benefits
Change in benefit obligation:
Defined Benefit Plan, Benefit Obligation, Contributions by Plan Participant	$ 100,000	$ 400,000