Pension Benefits - Fair Value Plan Assets Measurements (Details) - Pension Plans, Defined Benefit - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	$ 16.3	$ 315.8	$ 391.7
Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	16.2	268.1
Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0.0	45.9
Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0.0	0.0
United States Government and Government Agencies and Authorities
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		40.1
United States Government and Government Agencies and Authorities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		40.1
United States Government and Government Agencies and Authorities | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		0.0
United States Government and Government Agencies and Authorities | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		0.0
States and Political Subdivisions
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		0.1
States and Political Subdivisions | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		0.0
States and Political Subdivisions | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		0.1
States and Political Subdivisions | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		0.0
Corporate Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		45.4
Corporate Debt Securities [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		0.0
Corporate Debt Securities [Member] | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		45.4
Corporate Debt Securities [Member] | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		0.0
Bond Exchange Traded Funds
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		111.1
Bond Exchange Traded Funds | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		111.1
Bond Exchange Traded Funds | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		0.0
Bond Exchange Traded Funds | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		0.0
Partnership Interest [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0.1	1.8
Partnership Interest [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0.0	0.0
Partnership Interest [Member] | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0.0	0.0
Partnership Interest [Member] | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0.0	0.0
Short-term Investments
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	16.2	116.1
Short-term Investments | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	16.2	116.1
Short-term Investments | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0.0	0.0
Short-term Investments | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0.0	0.0
Receivables and Other
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		0.8
Receivables and Other | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		0.8
Receivables and Other | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		0.0
Receivables and Other | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		0.0
Debt Security, Government, Non-US [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		0.4
Debt Security, Government, Non-US [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		0.0
Debt Security, Government, Non-US [Member] | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		0.4
Debt Security, Government, Non-US [Member] | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		0.0
Fair Value, Inputs, Net Asset Value
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0.1	1.8
Fair Value, Inputs, Net Asset Value | United States Government and Government Agencies and Authorities
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		0.0
Fair Value, Inputs, Net Asset Value | States and Political Subdivisions
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		0.0
Fair Value, Inputs, Net Asset Value | Corporate Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		0.0
Fair Value, Inputs, Net Asset Value | Bond Exchange Traded Funds
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		0.0
Fair Value, Inputs, Net Asset Value | Partnership Interest [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0.1	1.8
Fair Value, Inputs, Net Asset Value | Short-term Investments
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	$ 0.0	0.0
Fair Value, Inputs, Net Asset Value | Receivables and Other
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		0.0
Fair Value, Inputs, Net Asset Value | Debt Security, Government, Non-US [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		$ 0.0