Earnings (Loss) Per Common Share - Computation of Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended						9 Months Ended
	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Mar. 31, 2021	Mar. 31, 2020
Earnings Per Share [Abstract]
Net earnings (loss)	$ 79.1	$ 148.5	$ 42.3	$ (284.4)	$ 37.8	$ 6.1	$ 269.9	$ (240.5)
Participating warrants dividend	0.0			(0.9)			0.0	(2.8)
Series A preferred stock dividend	0.0			(14.0)			0.0	(42.5)
Accretion of Series A preferred stock	0.0			(4.6)			0.0	(13.6)
Other securities dividends	0.0			(0.2)			0.0	(0.6)
Undistributed earnings allocated to participating securities	(4.1)			0.0			(13.6)	0.0
Earnings (loss) attributable to common shareholders	$ 75.0			$ (304.1)			$ 256.3	$ (300.0)
Basic weighted average common shares outstanding (in shares)	46.3			45.7			46.2	45.7
Basic earnings (loss) per common share (in usd per share)	$ 1.62			$ (6.65)			$ 5.55	$ (6.57)