Retirement Plans - Summary of Assets Measured at Fair Value Based on NAV Per Share (Details) - USD ($) $ in Millions		12 Months Ended
		Sep. 30, 2020	Sep. 30, 2019
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Defined Benefit Plans, Fair Value of Plan Assets		$ 2,123.2	$ 2,054.8
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments		228.9	113.1
Hedge Funds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Defined Benefit Plans, Fair Value of Plan Assets	[1]	$ 39.2	$ 42.9
Hedge Funds [Member] | Maximum [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Notice Period	[1]	30 days	30 days
Equity Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Defined Benefit Plans, Fair Value of Plan Assets	[2]	$ 1,416.9	$ 1,188.6
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	[2]	$ 228.9	$ 113.1
Equity Securities [Member] | Maximum [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Notice Period	[2]	60 days	60 days
Fixed Income Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Defined Benefit Plans, Fair Value of Plan Assets	[3]	$ 667.1	$ 823.3
Fixed Income Securities [Member] | Maximum [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Notice Period	[3]	10 days	10 days

[1] Hedge fund investments are primarily made through shares of limited partnerships or similar structures. Hedge funds are typically valued monthly by third-party administrators that have been appointed by the funds’ general partners.

[2] Commingled fund investments are valued at the NAV per share multiplied by the number of shares held. The determination of NAV for the commingled funds includes market pricing of the underlying assets as well as broker quotes and other valuation techniques.

[3] Fixed income and fixed income related instruments consist of commingled debt funds, which are valued at their NAV per share multiplied by the number of shares held. The determination of NAV for the commingled funds includes market pricing of the underlying assets as well as broker quotes and other valuation techniques.