Income tax - Schedule of Tax Character of Distributions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Ordinary income	$ 275.5	$ 203.7	$ 122.6
Long-term capital gains	$ 0.0	$ 43.1	$ 55.2