Earnings Per Common Share - Schedule of Basic and Diluted Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Basic Earnings Per Common Share:
Net (Loss) Income	$ (92.3)	$ (3.0)	$ 108.3	$ 218.9
Less: Provision for preferred dividends	3.7	1.6	11.1	1.6
(Loss) income allocated to participating securities	(0.1)		0.2	0.5
Net (Loss) Income Available to Common Shareholders	$ (95.9)	$ (4.6)	$ 97.0	$ 216.8
Weighted Average Common Shares Outstanding (in millions)	51.2	50.7	51.1	50.6
Basic (Loss) Earnings Per Common Share	$ (1.87)	$ (0.09)	$ 1.90	$ 4.28
Diluted Earnings Per Common Share:
Net (Loss) Income	$ (92.3)	$ (3.0)	$ 108.3	$ 218.9
Less: Provision for preferred dividends	3.7	1.6	11.1	1.6
(Loss) income allocated to participating securities	(0.1)		0.2	0.5
(Loss) Income Available to Common Shareholders	$ (95.9)	$ (4.6)	$ 97.0	$ 216.8
Weighted Average Common Shares Outstanding (in millions)	51.2	50.7	51.1	50.6
Dilutive Effect of Restricted Stock and Restricted Stock Units (in millions)			0.1	0.2
Weighted Average Diluted Common Shares (in millions)	51.2	50.7	51.2	50.8
Diluted (Loss) Earnings Per Common Share	$ (1.87)	$ (0.09)	$ 1.90	$ 4.27