Retirement and Postretirement Benefit Plans (Schedule of Postretirement Health Care Plan) (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Change in benefit obligation:
Benefit obligation at beginning of year	$ 380.4
Benefit obligation at end of year	371.8	$ 380.4
Amounts recorded in the Consolidated Balance Sheets:
Accrued benefits obligation, long-term	89.3	80.8
Postretirement Health Coverage [Member]
Change in benefit obligation:
Benefit obligation at beginning of year	12.7	17.0
Service cost	0.1	0.3
Interest cost	0.2	0.5
Actuarial gain	(0.4)	(4.1)
Defined Benefit Plan, Benefit Obligation, Benefits Paid	1.0	1.3
Defined Benefit Plan, Benefit Obligation, Contributions by Plan Participant	0.2	0.3
Benefit obligation at end of year	12.2	12.7
Amounts recorded in the Consolidated Balance Sheets:
Accrued benefits obligation, current portion	1.6	1.3
Accrued benefits obligation, long-term	10.6	11.4
Net amount recognized	12.2	$ 12.7
Special Termination Benefits
Change in benefit obligation:
Defined Benefit Plan, Benefit Obligation, Contributions by Plan Participant	$ 0.4