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Employee Benefit Plans - Summary of Amounts Recognized on the Consolidated Balance Sheets and in Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Pension Benefits
Amounts recognized in accumulated other comprehensive loss [Abstract]
Net gain (loss), net of taxes	$ (48.8)	$ (47.4)
Unrecognized prior service credit (cost), net of taxes	(0.1)	0.0
Total	(48.9)	(47.4)
Other Post-retirement Benefits
Amounts recognized in accumulated other comprehensive loss [Abstract]
Net gain (loss), net of taxes	(3.6)	0.2
Unrecognized prior service credit (cost), net of taxes	0.0	0.0
Total	(3.6)	0.2
Other Post-retirement Benefits | Non-qualified Plan Benefits
Amounts recognized in accumulated other comprehensive loss [Abstract]
Net gain (loss), net of taxes	(0.8)	(0.8)
Unrecognized prior service credit (cost), net of taxes	0.0	0.0
Total	$ (0.8)	$ (0.8)

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The net of tax net amount of gains and losses that are not yet recognized as a component of net periodic benefit cost, and that are recognized as increases or decreases in other comprehensive income as they arise. Gains and losses are due to changes in the value of either the benefit obligation or the plan assets resulting from experience different from that assumed or from a change in an actuarial assumption, or the consequence of a decision to temporarily deviate from the substantive plan.

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Amount related to the net of tax cost of benefit changes attributable to plan participants' prior service pursuant to a plan amendment or a plan initiation, which has not yet been recognized as components of net periodic benefit cost.

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

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (j)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 14A
-URI http://asc.fasb.org/extlink&oid=121641772&loc=SL7669686-108580

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 10A
-Subparagraph (i-k)
-URI http://asc.fasb.org/extlink&oid=121641772&loc=SL7669646-108580

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