Impairment and restructuring charges - Schedule of Impairment of Long-Lived Assets Held and Used by Asset (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended		12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Jun. 30, 2024	Sep. 30, 2025	Sep. 30, 2024	Dec. 31, 2024
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment of long-lived assets	$ 0.0	$ 0.0	$ 27.2	$ 0.0	$ 27.2	$ 27.2
Buildings, building improvements and leasehold improvements
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment of long-lived assets					7.8
Furniture and equipment
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment of long-lived assets					14.1
Software
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment of long-lived assets					0.2
Construction-in-progress
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment of long-lived assets					$ 5.1