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Segment Information Segments - Additional Information (Detail) $ in Millions	9 Months Ended
	Sep. 30, 2025 USD ($) Integer	Dec. 31, 2024 USD ($)
Segment Reporting Information
Goodwill	$ 354.0	$ 349.1
Number of Operating Segments | Integer	3
Unum International
Segment Reporting Information
Goodwill	$ 44.8	41.4
Unum US
Segment Reporting Information
Goodwill	281.5	280.0
Colonial Life
Segment Reporting Information
Goodwill	$ 27.7	$ 27.7

X

- Definition

Amount, after accumulated impairment loss, of asset representing future economic benefit arising from other asset acquired in business combination or from joint venture formation or both, that is not individually identified and separately recognized.

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