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Pension and Other Postretirement Benefits - Fair Value Hierarchy (Details) - Pension - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	$ 329.7	$ 318.8	$ 295.8
Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0.0	318.8
Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0.0	0.0
Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0.0	0.0
Assets measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	329.7	0.0
Cash
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	2.5
Cash | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0.0
Cash | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0.0
Cash | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0.0
Cash | Assets measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	2.5
Return Seeking Assets
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	245.6
Return Seeking Assets | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0.0
Return Seeking Assets | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0.0
Return Seeking Assets | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0.0
Return Seeking Assets | Assets measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	245.6
Global equity
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	167.8
Global equity | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0.0
Global equity | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0.0
Global equity | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0.0
Global equity | Assets measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	167.8
Diversified credit
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	49.2
Diversified credit | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0.0
Diversified credit | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0.0
Diversified credit | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0.0
Diversified credit | Assets measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	49.2
Real assets
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	28.6
Real assets | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0.0
Real assets | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0.0
Real assets | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0.0
Real assets | Assets measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	28.6
Liability hedging assets
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	81.6
Liability hedging assets | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0.0
Liability hedging assets | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0.0
Liability hedging assets | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0.0
Liability hedging assets | Assets measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	$ 81.6
U.S. equities
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets		98.4
U.S. equities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets		98.4
U.S. equities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets		0.0
U.S. equities | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets		0.0
U.S. equities | Assets measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets		0.0
International equities
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets		86.8
International equities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets		86.8
International equities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets		0.0
International equities | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets		0.0
International equities | Assets measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets		0.0
Fixed income
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets		133.6
Fixed income | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets		133.6
Fixed income | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets		0.0
Fixed income | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets		0.0
Fixed income | Assets measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets		$ 0.0

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Amount of asset segregated and restricted to provide benefit under defined benefit plan. Asset includes, but is not limited to, stock, bond, other investment, earning from investment, and contribution by employer and employee.

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