Commitments and Contingencies (Pace, Piedmont, Pasadena Narrative) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2012	Sep. 30, 2008	Sep. 30, 2006
Loss Contingencies [Line Items]
Pretax environmental expense		$ 18.3	$ 14.2	$ 12.8
Pre-tax loss from discontinued operations	$ 19.0	19.0
Pace, Florida
Loss Contingencies [Line Items]
Accrual for environmental loss contingencies		42.2					$ 42.0
Change in estimated exposure	$ 19.0
Pace, Florida | Discontinued Operations
Loss Contingencies [Line Items]
Pretax environmental expense							$ 42.0
Piedmont, South Carolina
Loss Contingencies [Line Items]
Accrual for environmental loss contingencies		13.3				$ 24.0
Piedmont, South Carolina | Discontinued Operations
Loss Contingencies [Line Items]
Pretax environmental expense						$ 24.0
Pasadena, Texas
Loss Contingencies [Line Items]
Accrual for environmental loss contingencies		$ 11.5
Total anticipated exposure					$ 13.0