Pensions and Other Postretirement Benefits (Details 7) - USD ($) $ in Millions		Apr. 30, 2023	Apr. 30, 2022	Apr. 30, 2021
Defined Benefit Plan Disclosure [Line Items]
Total financial assets measured at net asset value (G)	[1]	$ 0.0	$ 1.1
Defined Benefit Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Total financial assets measured at fair value		325.9	317.1	$ 397.8
Defined Benefit Pension Plans | Estimate of Fair Value Measurement
Defined Benefit Plan Disclosure [Line Items]
Total financial assets measured at fair value		325.9	316.0
Defined Benefit Pension Plans | Quoted Prices in Active Markets for Identical Assets (Level 1) | Estimate of Fair Value Measurement
Defined Benefit Plan Disclosure [Line Items]
Total financial assets measured at fair value		299.0	265.1
Defined Benefit Pension Plans | Significant Observable Inputs (Level 2) | Estimate of Fair Value Measurement
Defined Benefit Plan Disclosure [Line Items]
Total financial assets measured at fair value		26.9	50.9
Defined Benefit Pension Plans | Significant Unobservable Inputs (Level 3) | Estimate of Fair Value Measurement
Defined Benefit Plan Disclosure [Line Items]
Total financial assets measured at fair value		0.0	0.0
Defined Benefit Pension Plans | Cash and cash equivalents (A) | Estimate of Fair Value Measurement
Defined Benefit Plan Disclosure [Line Items]
Total financial assets measured at fair value	[2]	30.1	8.1
Defined Benefit Pension Plans | Cash and cash equivalents (A) | Quoted Prices in Active Markets for Identical Assets (Level 1) | Estimate of Fair Value Measurement
Defined Benefit Plan Disclosure [Line Items]
Total financial assets measured at fair value	[2]	30.1	8.1
Defined Benefit Pension Plans | Cash and cash equivalents (A) | Significant Observable Inputs (Level 2) | Estimate of Fair Value Measurement
Defined Benefit Plan Disclosure [Line Items]
Total financial assets measured at fair value	[2]	0.0	0.0
Defined Benefit Pension Plans | Cash and cash equivalents (A) | Significant Unobservable Inputs (Level 3) | Estimate of Fair Value Measurement
Defined Benefit Plan Disclosure [Line Items]
Total financial assets measured at fair value	[2]	0.0	0.0
Defined Benefit Pension Plans | U.S. (B) | Estimate of Fair Value Measurement
Defined Benefit Plan Disclosure [Line Items]
Total financial assets measured at fair value	[3]	2.6	29.8
Defined Benefit Pension Plans | U.S. (B) | Quoted Prices in Active Markets for Identical Assets (Level 1) | Estimate of Fair Value Measurement
Defined Benefit Plan Disclosure [Line Items]
Total financial assets measured at fair value	[3]	2.6	29.8
Defined Benefit Pension Plans | U.S. (B) | Significant Observable Inputs (Level 2) | Estimate of Fair Value Measurement
Defined Benefit Plan Disclosure [Line Items]
Total financial assets measured at fair value	[3]	0.0	0.0
Defined Benefit Pension Plans | U.S. (B) | Significant Unobservable Inputs (Level 3) | Estimate of Fair Value Measurement
Defined Benefit Plan Disclosure [Line Items]
Total financial assets measured at fair value	[3]	0.0	0.0
Defined Benefit Pension Plans | International (C) | Estimate of Fair Value Measurement
Defined Benefit Plan Disclosure [Line Items]
Total financial assets measured at fair value	[4]	6.7	33.3
Defined Benefit Pension Plans | International (C) | Quoted Prices in Active Markets for Identical Assets (Level 1) | Estimate of Fair Value Measurement
Defined Benefit Plan Disclosure [Line Items]
Total financial assets measured at fair value	[4]	6.7	33.3
Defined Benefit Pension Plans | International (C) | Significant Observable Inputs (Level 2) | Estimate of Fair Value Measurement
Defined Benefit Plan Disclosure [Line Items]
Total financial assets measured at fair value	[4]	0.0	0.0
Defined Benefit Pension Plans | International (C) | Significant Unobservable Inputs (Level 3) | Estimate of Fair Value Measurement
Defined Benefit Plan Disclosure [Line Items]
Total financial assets measured at fair value	[4]	0.0	0.0
Defined Benefit Pension Plans | Bonds (D) | Estimate of Fair Value Measurement
Defined Benefit Plan Disclosure [Line Items]
Total financial assets measured at fair value	[5]	259.6	187.3
Defined Benefit Pension Plans | Bonds (D) | Quoted Prices in Active Markets for Identical Assets (Level 1) | Estimate of Fair Value Measurement
Defined Benefit Plan Disclosure [Line Items]
Total financial assets measured at fair value	[5]	259.6	187.3
Defined Benefit Pension Plans | Bonds (D) | Significant Observable Inputs (Level 2) | Estimate of Fair Value Measurement
Defined Benefit Plan Disclosure [Line Items]
Total financial assets measured at fair value	[5]	0.0	0.0
Defined Benefit Pension Plans | Bonds (D) | Significant Unobservable Inputs (Level 3) | Estimate of Fair Value Measurement
Defined Benefit Plan Disclosure [Line Items]
Total financial assets measured at fair value	[5]	0.0	0.0
Defined Benefit Pension Plans | Fixed income (E) | Estimate of Fair Value Measurement
Defined Benefit Plan Disclosure [Line Items]
Total financial assets measured at fair value	[6]		6.6
Defined Benefit Pension Plans | Fixed income (E) | Quoted Prices in Active Markets for Identical Assets (Level 1) | Estimate of Fair Value Measurement
Defined Benefit Plan Disclosure [Line Items]
Total financial assets measured at fair value	[6]		6.6
Defined Benefit Pension Plans | Fixed income (E) | Significant Observable Inputs (Level 2) | Estimate of Fair Value Measurement
Defined Benefit Plan Disclosure [Line Items]
Total financial assets measured at fair value	[6]		0.0
Defined Benefit Pension Plans | Fixed income (E) | Significant Unobservable Inputs (Level 3) | Estimate of Fair Value Measurement
Defined Benefit Plan Disclosure [Line Items]
Total financial assets measured at fair value	[6]		0.0
Defined Benefit Pension Plans | Other types of investments (F) | Estimate of Fair Value Measurement
Defined Benefit Plan Disclosure [Line Items]
Total financial assets measured at fair value	[7]	26.9	50.9
Defined Benefit Pension Plans | Other types of investments (F) | Quoted Prices in Active Markets for Identical Assets (Level 1) | Estimate of Fair Value Measurement
Defined Benefit Plan Disclosure [Line Items]
Total financial assets measured at fair value	[7]	0.0	0.0
Defined Benefit Pension Plans | Other types of investments (F) | Significant Observable Inputs (Level 2) | Estimate of Fair Value Measurement
Defined Benefit Plan Disclosure [Line Items]
Total financial assets measured at fair value	[7]	26.9	50.9
Defined Benefit Pension Plans | Other types of investments (F) | Significant Unobservable Inputs (Level 3) | Estimate of Fair Value Measurement
Defined Benefit Plan Disclosure [Line Items]
Total financial assets measured at fair value	[7]	$ 0.0	$ 0.0

[1] This category was composed of a private equity fund that consisted primarily of limited partnership interests in corporate finance and venture capital funds, as well as a private limited investment partnership. The fair value estimates of the private equity fund and private limited investment partnership were based on the underlying funds’ net asset values. Furthermore, as a practical expedient equivalent to our defined benefit plan’s ownership interest in the partners’ capital, a proportionate share of the net assets was attributed and further corroborated by our review. The private equity fund and private limited investment partnership were non-redeemable, and the return of principal was based on the liquidation of the underlying assets. In accordance with ASU 2015-07, the private equity fund and private limited investment partnership were removed from the total financial assets measured at fair value and disclosed separately.

[2] This category includes money market holdings with maturities of three months or less and are classified as Level 1 assets. Based on the short-term nature of these assets, carrying value approximates fair value.

[3] This category is invested in a diversified portfolio of common stocks and index funds that primarily invest in U.S. stocks with broad market capitalization ranges similar to those found in the S&P 500 Index and/or the various Russell Indices, and are traded on active exchanges. The Level 1 assets are valued using quoted market prices for identical securities in active markets.

[4] This category is invested primarily in common stocks and other equity securities traded on active exchanges of foreign issuers located outside the U.S. The fund invests primarily in developed countries, but may also invest in emerging markets. The Level 1 assets are valued using quoted market prices for identical securities in active markets.

[5] This category is primarily composed of bond funds, which seek to duplicate the return characteristics of high-quality U.S. and foreign corporate bonds with a duration range of 10 to 13 years, as well as various U.S. Treasury Separate Trading of Registered Interest and Principal holdings, with wide-ranging maturity dates. These assets are valued using quoted market prices for identical securities in active markets and are classified as Level 1 assets.

[6] This category was composed of fixed-income funds that were invested primarily in government-related bonds of non-U.S. issuers and included investments in the Canadian, as well as emerging markets. These assets were valued using quoted market prices for identical securities in active markets and were classified as Level 1 assets.

[7] This category is composed of a real estate fund whereby the underlying investments are contained in the Canadian market and a common collective trust fund investing in direct commercial property funds. The real estate fund and the collective trust fund investing in direct commercial property are classified as Level 2 assets, whereby the underlying securities are valued utilizing quoted market prices for identical securities in active markets and based on the quoted market prices of the underlying investments in the common collective trust, respectively.