Income taxes - Tax Loss Carryforwards (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Income Tax Disclosure [Abstract]
U.S. Federal	$ 366.0
State and local	180.2
Foreign	266.8
Total tax loss carryforwards	813.0	$ 825.5
Operating Loss Carryforwards [Line Items]
Tax loss carryforwards, not set to expire	271.1
Total tax loss carryforwards	813.0	$ 825.5
2024
Operating Loss Carryforwards [Line Items]
Tax loss carryforwards, set to expire	13.4
2025
Operating Loss Carryforwards [Line Items]
Tax loss carryforwards, set to expire	20.8
2026
Operating Loss Carryforwards [Line Items]
Tax loss carryforwards, set to expire	15.6
2027
Operating Loss Carryforwards [Line Items]
Tax loss carryforwards, set to expire	40.8
2028
Operating Loss Carryforwards [Line Items]
Tax loss carryforwards, set to expire	93.1
Thereafter
Operating Loss Carryforwards [Line Items]
Tax loss carryforwards, set to expire	$ 358.2