Retirement Benefits - Fair Value Pension Plan Assets (Details) - Pension Benefits - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 515.4	$ 765.6	$ 805.1
Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	9.8	8.9
Equity Mutual Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	21.5	31.7
Common Pooled Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	84.5	123.3
U.S. Treasuries
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	47.2	55.0
State and Local Municipal Bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	6.4	6.2
Sovereign Debt
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4.9	7.1
Corporate Bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	105.5	141.6
Fixed Income Mutual Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	41.8	55.5
Common Pooled Fixed Income Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	174.2	306.3
Alternative Investment Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2.1	7.1
Common Pooled Fund
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	17.5	22.9
Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	67.2	96.6
Quoted Prices in Active Markets for Identical Assets (Level 1) | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3.5	8.9
Quoted Prices in Active Markets for Identical Assets (Level 1) | Equity Mutual Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	21.5	31.7
Quoted Prices in Active Markets for Identical Assets (Level 1) | Common Pooled Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. Treasuries
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Quoted Prices in Active Markets for Identical Assets (Level 1) | State and Local Municipal Bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Sovereign Debt
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporate Bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed Income Mutual Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	41.8	55.5
Quoted Prices in Active Markets for Identical Assets (Level 1) | Common Pooled Fixed Income Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Alternative Investment Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Common Pooled Fund
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.4	0.5
Quoted Prices in Active Markets for Similar Assets (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	420.6	630.8
Quoted Prices in Active Markets for Similar Assets (Level 2) | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	6.3	0.0
Quoted Prices in Active Markets for Similar Assets (Level 2) | Equity Mutual Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Quoted Prices in Active Markets for Similar Assets (Level 2) | Common Pooled Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	84.5	123.3
Quoted Prices in Active Markets for Similar Assets (Level 2) | U.S. Treasuries
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	47.2	55.0
Quoted Prices in Active Markets for Similar Assets (Level 2) | State and Local Municipal Bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	6.4	6.2
Quoted Prices in Active Markets for Similar Assets (Level 2) | Sovereign Debt
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4.9	7.1
Quoted Prices in Active Markets for Similar Assets (Level 2) | Corporate Bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	105.5	141.6
Quoted Prices in Active Markets for Similar Assets (Level 2) | Fixed Income Mutual Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Quoted Prices in Active Markets for Similar Assets (Level 2) | Common Pooled Fixed Income Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	148.7	275.2
Quoted Prices in Active Markets for Similar Assets (Level 2) | Alternative Investment Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Quoted Prices in Active Markets for Similar Assets (Level 2) | Common Pooled Fund
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	17.1	22.4
Unobservable inputs for which little or no market data exists (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Unobservable inputs for which little or no market data exists (Level 3) | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Unobservable inputs for which little or no market data exists (Level 3) | Equity Mutual Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Unobservable inputs for which little or no market data exists (Level 3) | Common Pooled Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Unobservable inputs for which little or no market data exists (Level 3) | U.S. Treasuries
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Unobservable inputs for which little or no market data exists (Level 3) | State and Local Municipal Bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Unobservable inputs for which little or no market data exists (Level 3) | Sovereign Debt
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Unobservable inputs for which little or no market data exists (Level 3) | Corporate Bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Unobservable inputs for which little or no market data exists (Level 3) | Fixed Income Mutual Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Unobservable inputs for which little or no market data exists (Level 3) | Common Pooled Fixed Income Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Unobservable inputs for which little or no market data exists (Level 3) | Alternative Investment Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Unobservable inputs for which little or no market data exists (Level 3) | Common Pooled Fund
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Investments Priced Using Net Asset Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	27.6	38.2
Investments Priced Using Net Asset Value | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Investments Priced Using Net Asset Value | Equity Mutual Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Investments Priced Using Net Asset Value | Common Pooled Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Investments Priced Using Net Asset Value | U.S. Treasuries
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Investments Priced Using Net Asset Value | State and Local Municipal Bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Investments Priced Using Net Asset Value | Sovereign Debt
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Investments Priced Using Net Asset Value | Corporate Bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Investments Priced Using Net Asset Value | Fixed Income Mutual Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Investments Priced Using Net Asset Value | Common Pooled Fixed Income Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	25.5	31.1
Investments Priced Using Net Asset Value | Alternative Investment Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2.1	7.1
Investments Priced Using Net Asset Value | Common Pooled Fund
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 0.0	$ 0.0