Earnings per Common Share - Schedule of Calculations of Basic and Diluted Earnings from Continuing Operations per Common 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 income									$ 188.5	$ 47.0	$ 11.3
Less: earnings and dividends allocated to participating securities									(1.7)	(0.3)	(0.1)
Earnings available for common shareholders used in calculation of basic earnings per share									$ 186.8	$ 46.7	$ 11.2
Weighted average number of common shares outstanding, basic (in shares)	47.4	47.2	47.2	47.1	47.1	47.0	47.0	46.9	47.2	47.0	48.1
Basic earnings per common share (in dollars per share)	$ 0.90	$ 0.63	$ 1.93	$ 0.49	$ 0.54	$ 0.44	$ 0.15	$ (0.13)	$ 3.96	$ 0.99	$ 0.23
Earnings available for common shareholders used in calculation of diluted earnings per share									$ 186.8	$ 46.7	$ 11.2
Effect of shares issuable under share-based compensation plans (in shares)									0.4	0.1	0.1
Weighted average number of common shares outstanding, diluted (in shares)	48.0	47.7	47.6	47.3	47.1	47.1	47.1	46.9	47.6	47.1	48.2
Diluted earnings per common share (in dollars per share)	$ 0.88	$ 0.63	$ 1.92	$ 0.49	$ 0.54	$ 0.44	$ 0.15	$ (0.13)	$ 3.92	$ 0.99	$ 0.23