Retirement Benefits - Fair Value Pension Plan Assets (Details) - Pension Benefits - USD ($) $ in Millions | Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019 |
Defined Benefit Plan Disclosure [Line Items] | | | |
Fair value of plan assets | $ 765.6 | $ 805.1 | $ 743.4 |
Cash and cash equivalents | | | |
Defined Benefit Plan Disclosure [Line Items] | | | |
Fair value of plan assets | 8.9 | 26.6 | |
Equity Mutual Funds | | | |
Defined Benefit Plan Disclosure [Line Items] | | | |
Fair value of plan assets | 31.7 | 29.8 | |
Common Pooled Equity Funds | | | |
Defined Benefit Plan Disclosure [Line Items] | | | |
Fair value of plan assets | 123.3 | 153.9 | |
U.S. Treasuries | | | |
Defined Benefit Plan Disclosure [Line Items] | | | |
Fair value of plan assets | 55 | 52 | |
State and Local Municipal Bonds | | | |
Defined Benefit Plan Disclosure [Line Items] | | | |
Fair value of plan assets | 6.2 | 9.3 | |
Sovereign Debt | | | |
Defined Benefit Plan Disclosure [Line Items] | | | |
Fair value of plan assets | 7.1 | 9.3 | |
Corporate Bonds | | | |
Defined Benefit Plan Disclosure [Line Items] | | | |
Fair value of plan assets | 141.6 | 145.1 | |
Fixed Income Mutual Funds | | | |
Defined Benefit Plan Disclosure [Line Items] | | | |
Fair value of plan assets | 55.5 | 59.9 | |
Common Pooled Fixed Income Funds | | | |
Defined Benefit Plan Disclosure [Line Items] | | | |
Fair value of plan assets | 306.3 | 279.4 | |
Alternative Investment Funds | | | |
Defined Benefit Plan Disclosure [Line Items] | | | |
Fair value of plan assets | 7.1 | 14.3 | |
Common Pooled Fund | | | |
Defined Benefit Plan Disclosure [Line Items] | | | |
Fair value of plan assets | 22.9 | 25.5 | |
Quoted Prices in Active Markets for Identical Assets (Level 1) | | | |
Defined Benefit Plan Disclosure [Line Items] | | | |
Fair value of plan assets | 96.6 | 116.8 | |
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 | 8.9 | 26.6 | |
Quoted Prices in Active Markets for Identical Assets (Level 1) | Equity Mutual Funds | | | |
Defined Benefit Plan Disclosure [Line Items] | | | |
Fair value of plan assets | 31.7 | 29.8 | |
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 | |
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 | |
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 | |
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 | |
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 | |
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 | 55.5 | 59.9 | |
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 | |
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 | |
Quoted Prices in Active Markets for Identical Assets (Level 1) | Common Pooled Fund | | | |
Defined Benefit Plan Disclosure [Line Items] | | | |
Fair value of plan assets | 0.5 | 0.5 | |
Quoted Prices in Active Markets for Similar Assets (Level 2) | | | |
Defined Benefit Plan Disclosure [Line Items] | | | |
Fair value of plan assets | 630.8 | 674 | |
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 | 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 | |
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 | 123.3 | 153.9 | |
Quoted Prices in Active Markets for Similar Assets (Level 2) | U.S. Treasuries | | | |
Defined Benefit Plan Disclosure [Line Items] | | | |
Fair value of plan assets | 55 | 52 | |
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 | 6.2 | 9.3 | |
Quoted Prices in Active Markets for Similar Assets (Level 2) | Sovereign Debt | | | |
Defined Benefit Plan Disclosure [Line Items] | | | |
Fair value of plan assets | 7.1 | 9.3 | |
Quoted Prices in Active Markets for Similar Assets (Level 2) | Corporate Bonds | | | |
Defined Benefit Plan Disclosure [Line Items] | | | |
Fair value of plan assets | 141.6 | 145.1 | |
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 | |
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 | 275.2 | 279.4 | |
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 | |
Quoted Prices in Active Markets for Similar Assets (Level 2) | Common Pooled Fund | | | |
Defined Benefit Plan Disclosure [Line Items] | | | |
Fair value of plan assets | 22.4 | 25 | |
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 | |
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 | |
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 | |
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 | |
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 | |
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 | |
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 | |
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 | |
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 | |
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 | |
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 | |
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 | |
Investments Priced Using Net Asset Value | | | |
Defined Benefit Plan Disclosure [Line Items] | | | |
Fair value of plan assets | 38.2 | 14.3 | |
Investments Priced Using Net Asset Value | Cash and cash equivalents | | | |
Defined Benefit Plan Disclosure [Line Items] | | | |
Fair value of plan assets | 0 | 0 | |
Investments Priced Using Net Asset Value | Equity Mutual Funds | | | |
Defined Benefit Plan Disclosure [Line Items] | | | |
Fair value of plan assets | 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 | |
Investments Priced Using Net Asset Value | U.S. Treasuries | | | |
Defined Benefit Plan Disclosure [Line Items] | | | |
Fair value of plan assets | 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 | |
Investments Priced Using Net Asset Value | Sovereign Debt | | | |
Defined Benefit Plan Disclosure [Line Items] | | | |
Fair value of plan assets | 0 | 0 | |
Investments Priced Using Net Asset Value | Corporate Bonds | | | |
Defined Benefit Plan Disclosure [Line Items] | | | |
Fair value of plan assets | 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 | |
Investments Priced Using Net Asset Value | Common Pooled Fixed Income Funds | | | |
Defined Benefit Plan Disclosure [Line Items] | | | |
Fair value of plan assets | 31.1 | 0 | |
Investments Priced Using Net Asset Value | Alternative Investment Funds | | | |
Defined Benefit Plan Disclosure [Line Items] | | | |
Fair value of plan assets | 7.1 | 14.3 | |
Investments Priced Using Net Asset Value | Common Pooled Fund | | | |
Defined Benefit Plan Disclosure [Line Items] | | | |
Fair value of plan assets | $ 0 | $ 0 | |