Variable and voting interest entities - Reconciliation of noncontrolling interests (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2023	Mar. 31, 2022
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Balance, beginning of period	$ 7.9	$ (0.4)
Net income (loss) attributable to noncontrolling interests	2.4	(0.3)
Contributions (Redemptions)	1.1	0.0
Balance, end of period	$ 11.4	$ (0.7)

Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which is directly or indirectly attributable to that ownership interest in subsidiary equity which is not attributable to the parent (that is, noncontrolling interest, previously referred to as minority interest).

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+ Details