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Consolidated Statements of Income and Comprehensive Income (Parenthetical) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
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Sep. 30, 2021 | Sep. 30, 2020 | Sep. 30, 2021 | Sep. 30, 2020
Income Statement [Abstract] |  |  |  |
Changes in unrealized losses on marketable debt securities, tax | $ 0.0 | $ 0.1 | $ 0.1 | $ 0.2
Amortization of pension and postretirement plans actuarial loss and prior service cost, tax | $ 0.8 | $ 0.9 | $ 2.5 | $ 2.7

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- Definition Tax effect of the adjustment out of other comprehensive income for prior service costs and net loss recognized as a component of net periodic benefit cost during the period. + References No definition available. + Details
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- Definition Amount, before adjustment, of tax expense (benefit) for unrealized holding gain (loss) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). Excludes tax expense (benefit) for unrealized gain (loss) on investment in debt security measured at amortized cost (held-to-maturity) from transfer to available-for-sale. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=124509347&loc=d3e640-108580 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 10A -Subparagraph (f) -URI http://asc.fasb.org/extlink&oid=124509347&loc=SL7669646-108580 + Details
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