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CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Parenthetical) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Pension Plans [Member]      
Pension Plan and Restoration of Retirement Income Plan:      
Amortization of prior service cost, net of tax of $0.1, $0.1 and $0.1, respectively $ 0.1 $ 0.1 $ 0.1
Amortization of deferred net loss, net of tax of $0.1, $0.2 and $0.2, respectively 0.1 0.2 0.2
Net (loss) gain arising during the period, net of tax of $0.0, $1.0 and ($2.4), respectively 0.0 1.0 (2.4)
Regulatory classification of certain pension costs, net of tax of $1.2, $0.0 and $0.0, respectively 1.2 0.0 0.0
Settlement cost, net of tax of $0.0, $0.4 and $4.3, respectively 0.0 0.4 4.3
Other Postretirement Benefits Plan [Member]      
Postretirement plans:      
Amortization of prior service credit, net of tax of $0.0, $0.0 and ($0.1), respectively 0.0 0.0 (0.1)
Amortization of deferred net gain, net of tax of $(0.1), ($0.1) and $0.0, respectively (0.1) (0.1) 0.0
Net gain (loss) arising during the period, net of tax of $0.2, ($0.2) and $1.7, respectively $ 0.2 $ (0.2) $ 1.7