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Discontinued operations - Summary (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Income
Income from discontinued operations, net of tax	$ 0.0	$ 0.0	$ 1,068.4
U.S. Federal Business \| Discontinued Operation, Disposed of by Sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenue			149.5
Income
Operations			8.4
Gain on sale			1,060.7
Income (loss) from discontinued operation			1,069.1
Income tax provision			0.7
Income from discontinued operations, net of tax			$ 1,068.4