Significant Accounting Policies - Basic and Diluted Earnings from Continuing Operations Per Common Share (Detail) - shares shares in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Earnings Per Share [Abstract]
Basic weighted-average common shares outstanding	61.1	61.8	61.5	61.9
Effect of dilutive employee and director awards	0.2	0.2	0.1	0.2
Diluted weighted-average common shares outstanding	61.3	62.0	61.6	62.1

No definition available.

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- Definition

Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of share based payment arrangements using the treasury stock method.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
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-Name Accounting Standards Codification
-Section 45
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-URI https://asc.fasb.org/1943274/2147480454/718-10-45-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 260
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 260
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 260
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 260
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-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482689/260-10-45-28A

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- Definition

The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 260
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482662/260-10-50-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 260
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-Section 45
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- Definition

Number of [basic] shares or units, after adjustment for contingently issuable shares or units and other shares or units not deemed outstanding, determined by relating the portion of time within a reporting period that common shares or units have been outstanding to the total time in that period.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 260
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482662/260-10-50-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 260
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-Publisher FASB
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