Retirement Benefits - Schedule of Fair Value of Pension Plan Assets and Liabilities by Asset Category and by Level (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	$ 604.5	$ 605.9
Receivables	9.5	0.9
Defined Benefit Plan, Plan Assets, Accounts Payable	(17.7)	(19.1)
Total assets	1,005.0	957.0
Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.1	0.4
Domestic equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	428.5	406.3
International equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	44.2	37.0
Corporate debt securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	57.5	71.5
Asset-backed securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	29.3	28.7
U.S. government securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	28.8	41.4
Municipal bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets		0.6
Foreign bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.9	0.5
Derivatives
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.1
Registered investment companies
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	13.9	16.4
Private assets
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	1.2	3.1
Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	486.7	454.0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.1	0.4
Quoted Prices in Active Markets for Identical Assets (Level 1) | Domestic equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	428.5	400.2
Quoted Prices in Active Markets for Identical Assets (Level 1) | International equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	44.2	37.0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporate debt securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Asset-backed securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. government securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Municipal bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets		0.0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Foreign bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Derivatives
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Registered investment companies
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	13.9	16.4
Quoted Prices in Active Markets for Identical Assets (Level 1) | Private assets
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	99.0	110.8
Other Observable Inputs (Level 2) | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Other Observable Inputs (Level 2) | Domestic equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Other Observable Inputs (Level 2) | International equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Other Observable Inputs (Level 2) | Corporate debt securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	39.9	39.6
Other Observable Inputs (Level 2) | Asset-backed securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	29.3	28.7
Other Observable Inputs (Level 2) | U.S. government securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	28.8	41.4
Other Observable Inputs (Level 2) | Municipal bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets		0.6
Other Observable Inputs (Level 2) | Foreign bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.9	0.5
Other Observable Inputs (Level 2) | Derivatives
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.1
Other Observable Inputs (Level 2) | Registered investment companies
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Other Observable Inputs (Level 2) | Private assets
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	18.8	41.1
Total assets	18.8	41.1	$ 37.2
Unobservable Inputs (Level 3) | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Unobservable Inputs (Level 3) | Domestic equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	6.1
Total assets	0.0	6.1	4.2
Unobservable Inputs (Level 3) | International equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Unobservable Inputs (Level 3) | Corporate debt securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	17.6	31.9
Total assets	17.6	31.9	27.6
Unobservable Inputs (Level 3) | Asset-backed securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Unobservable Inputs (Level 3) | U.S. government securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Unobservable Inputs (Level 3) | Municipal bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets		0.0
Unobservable Inputs (Level 3) | Foreign bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Unobservable Inputs (Level 3) | Derivatives
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0
Unobservable Inputs (Level 3) | Registered investment companies
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	0.0	0.0
Unobservable Inputs (Level 3) | Private assets
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	1.2	3.1
Total assets	1.2	3.1	$ 5.4
NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	408.7	369.3
NAV | Common/collective trusts ("CCTs")
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	56.4	36.2
NAV | Private assets
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	97.8	100.8
NAV | Hedge funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension plan assets	$ 254.5	$ 232.3