Pension and Other Postretirement Benefit Costs - Narrative - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020
Pension and Other Postretirement Benefits Cost (Reversal of Cost) [Abstract]
Employer contributions	$ 2.6	$ 2.5
Estimated future employer contributions in next fiscal year	15.6
Defined benefit pension plan cash contributions	$ 4.5

Amount of contribution expected to be received by defined benefit plan from employer in remainder of current fiscal year. Excludes contribution previously paid by employer in current fiscal year.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 6
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e2709-114920

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 55
-Paragraph 18
-URI http://asc.fasb.org/extlink&oid=118257860&loc=d3e4587-114921

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- Definition

Amount of cost for defined contribution plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 70
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942

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- Definition

Amount of cash outflow for pension and other postretirement benefits. Includes, but is not limited to, employer contribution to fund plan asset and payment to retiree.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 25
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3536-108585

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