Earnings Per Common Share (Summary of Calculations of Earnings per Share) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2016
Earnings Per Share [Abstract]
Net earnings									$ 99.4	$ 188.9	$ 33.9
Participating warrant dividend									1.8	0.0	0.0
Preferred stock dividend									22.9	0.0	0.0
Accretion of Series A preferred stock									7.2	0.0	0.0
Other securities dividends									1.1	0.0	0.0
Basic earnings attributable to common shareholders									$ 66.4	$ 188.9	$ 33.9
Basic average common shares outstanding (in shares)									44.9	44.6	44.6
Basic earnings per common share (in dollars per share)	$ (0.06)	$ (2.74)	$ 3.55	$ 0.75	$ 0.97	$ 0.89	$ 1.61	$ 0.76	$ 1.48	$ 4.23	$ 0.76
Dilutive effect of stock options and equivalents (in shares)									0.3	0.8	0.8
Diluted weighted-average shares outstanding (in shares)									45.2	45.4	45.4
Diluted earnings attributable to common shareholders									$ 66.4	$ 188.9	$ 33.9
Diluted earnings per common share (in dollars per share)	$ (0.06)	$ (2.74)	$ 3.49	$ 0.73	$ 0.95	$ 0.87	$ 1.58	$ 0.75	$ 1.47	$ 4.16	$ 0.75