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Employee Benefits - Amount of Loss Recognized in Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Salaried VEBA
Defined Benefit Plan Disclosure [Line Items]
Accumulated net actuarial loss	$ (11.2)	$ (12.1)
Prior service cost	(24.1)	(41.1)
Cumulative loss reflected in Accumulated other comprehensive loss	(35.3)	(53.2)
Canadian pension plan | Canadian pension plan
Defined Benefit Plan Disclosure [Line Items]
Accumulated net actuarial loss	(2.1)	(1.9)
Cumulative loss reflected in Accumulated other comprehensive loss	$ (2.1)	$ (1.9)

X

- Definition

Amount, before tax, of accumulated other comprehensive (income) loss for defined benefit plan, that has not been recognized in net periodic benefit cost (credit).

+ References

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-Publisher FASB
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- Definition

Amount, before tax, of accumulated other comprehensive income (loss) for gain (loss) of defined benefit plan, that has not been recognized in net periodic benefit (cost) credit.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (j)
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- Definition

Amount, before tax, of accumulated other comprehensive (income) loss for cost (credit) of benefit change attributable to participants' prior service from plan amendment or plan initiation of defined benefit plan, that has not been recognized in net periodic benefit cost (credit).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
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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.

+ References

No definition available.

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