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Pension and Other Postretirement Benefit Plans - Recurring Fair Value Measures (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Pension
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	$ 589.0	$ 568.6	$ 745.7
Pension | Level 1
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	155.0	134.3
Pension | Level 2
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	415.1	411.9
Pension | Level 3
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	18.9	22.4
Pension | U.S. Large-cap
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	83.7	61.2
Pension | U.S. Large-cap | Level 1
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	0.0
Pension | U.S. Large-cap | Level 2
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	83.7	61.2
Pension | U.S. Large-cap | Level 3
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	0.0
Pension | U.S. Mid-cap Growth
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	69.9	40.0
Pension | U.S. Mid-cap Growth | Level 1
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	0.0
Pension | U.S. Mid-cap Growth | Level 2
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	69.9	40.0
Pension | U.S. Mid-cap Growth | Level 3
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	0.0
Pension | U.S. Small-cap
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	46.5	35.4
Pension | U.S. Small-cap | Level 1
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	0.0
Pension | U.S. Small-cap | Level 2
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	46.5	35.4
Pension | U.S. Small-cap | Level 3
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	0.0
Pension | International
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	134.6	127.0
Pension | International | Level 1
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	134.6	127.0
Pension | International | Level 2
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	0.0
Pension | International | Level 3
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	0.0
Pension | Fixed Income Securities
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	215.0	275.3
Pension | Fixed Income Securities | Level 1
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	0.0
Pension | Fixed Income Securities | Level 2
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	215.0	275.3
Pension | Fixed Income Securities | Level 3
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	0.0
Pension | Cash and Cash Equivalents
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	20.4	7.3
Pension | Cash and Cash Equivalents | Level 1
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	20.4	7.3
Pension | Cash and Cash Equivalents | Level 2
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	0.0
Pension | Cash and Cash Equivalents | Level 3
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	0.0
Pension | Real Estate
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	18.9	22.4
Pension | Real Estate | Level 1
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	0.0
Pension | Real Estate | Level 2
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	0.0
Pension | Real Estate | Level 3
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	18.9	22.4	21.6
Postretirement Health and Life
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	173.8	162.6	201.8
Postretirement Health and Life | Level 1
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	173.8	162.6
Postretirement Health and Life | Level 2
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	0.0
Postretirement Health and Life | Level 3
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	0.0
Postretirement Health and Life | U.S. Large-cap
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	30.0	26.7
Postretirement Health and Life | U.S. Large-cap | Level 1
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	30.0	26.7
Postretirement Health and Life | U.S. Large-cap | Level 2
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	0.0
Postretirement Health and Life | U.S. Large-cap | Level 3
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	0.0
Postretirement Health and Life | U.S. Mid-cap Growth
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	28.7	25.5
Postretirement Health and Life | U.S. Mid-cap Growth | Level 1
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	28.7	25.5
Postretirement Health and Life | U.S. Mid-cap Growth | Level 2
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	0.0
Postretirement Health and Life | U.S. Mid-cap Growth | Level 3
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	0.0
Postretirement Health and Life | U.S. Small-cap
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	14.9	12.7
Postretirement Health and Life | U.S. Small-cap | Level 1
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	14.9	12.7
Postretirement Health and Life | U.S. Small-cap | Level 2
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	0.0
Postretirement Health and Life | U.S. Small-cap | Level 3
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	0.0
Postretirement Health and Life | International
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	41.9	41.5
Postretirement Health and Life | International | Level 1
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	41.9	41.5
Postretirement Health and Life | International | Level 2
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	0.0
Postretirement Health and Life | International | Level 3
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	0.0
Postretirement Health and Life | Cash and Cash Equivalents
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	3.2	0.7
Postretirement Health and Life | Cash and Cash Equivalents | Level 1
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	3.2	0.7
Postretirement Health and Life | Cash and Cash Equivalents | Level 2
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	0.0
Postretirement Health and Life | Cash and Cash Equivalents | Level 3
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	0.0
Postretirement Health and Life | Private Equity | Level 3
Recurring Fair Value Measures [Line Items]
Fair Value of Assets		0.0	$ 2.0
Postretirement Health and Life | Mutual Funds
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	55.1	55.5
Postretirement Health and Life | Mutual Funds | Level 1
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	55.1	55.5
Postretirement Health and Life | Mutual Funds | Level 2
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	0.0
Postretirement Health and Life | Mutual Funds | Level 3
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	$ 0.0	$ 0.0

X

- Definition

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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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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