Quarterly Financial Information (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 705.3	$ 767.5	$ 723.2	$ 685.0	$ 782.8	$ 726.8	$ 714.2	$ 683.5	$ 2,881.0	$ 2,907.3	$ 2,848.0
Divisional income	66.2	135.3	87.3	78.9	94.1	69.9	81.3	70.8	367.7	316.1	289.4
Net Income	$ 42.4	$ 93.9	$ 46.9	$ 39.8	$ 27.9	$ 32.6	$ 49.5	$ 42.2	$ 223.0	$ 152.2	$ 252.4
Net Income Attributable to Common Shareholders per Common Share - Basic (usd per share)	$ 0.64	$ 1.41	$ 0.70	$ 0.60	$ 0.42	$ 490,000	$ 740,000	$ 630,000	$ 3.35	$ 2.28	$ 3.81
Net Income Attributable to Common Shareholders per Common Share - Diluted (usd per share)	$ 0.63	$ 1.40	$ 0.70	$ 0.59	$ 0.41	$ 480,000	$ 740,000	$ 620,000	$ 3.32	$ 2.25	$ 3.73