Benefit Plans, Amounts Recognized in Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Amounts recognized in accumulated other comprehensive income [Abstract]
Amount recognized end of year	$ 114.9	$ 96.1
Accumulated benefit obligation	501.7	450.5
Pension Benefits [Member]
Amounts recognized in accumulated other comprehensive income [Abstract]
Net actuarial (gain) loss	119.0	99.6
Prior service cost	0.1	0.1
Amount recognized end of year	119.1	99.7
Post-Retirement Benefits [Member]
Amounts recognized in accumulated other comprehensive income [Abstract]
Net actuarial (gain) loss	(4.2)	(3.7)
Prior service cost	0.0	0.0
Amount recognized end of year	$ (4.2)	$ (3.7)

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

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

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-Topic 220
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- Definition

Amount of actuarial present value of benefits attributed to employee service rendered, excluding assumptions about future compensation level.

+ References

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- Definition

Amount, after 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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 14A
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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- Definition

Amount, after 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
-SubTopic 20
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-Paragraph 1
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