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Held for Sale and Discontinued Operations - Narrative (Details) £ in Millions, $ in Millions			3 Months Ended			9 Months Ended
	Apr. 12, 2021 USD ($)	Apr. 12, 2021 GBP (£)	Sep. 30, 2021 USD ($)	Mar. 31, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net gain from sale of discontinued operations, net of tax			$ 0.0		$ (0.7)	$ 18.7	$ (0.8)
Loss on sale				$ 28.7
Discontinued Operations, Disposed of by Sale | Sirius Group
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Liability related to sale								$ 18.7
Net gain from sale of discontinued operations, net of tax						17.6
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Fresh Insurance Services Group Limited
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of business	$ 1.5	£ 1.1
Disposal Group, Held-for-sale, Not Discontinued Operations | Fresh Insurance Services Group Limited
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loss on sale				$ 28.7
Foreign Currency Gain (Loss) | Discontinued Operations, Disposed of by Sale | Sirius Group
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net gain from sale of discontinued operations, net of tax						$ 1.1

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