Schedule V - Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Premiums receivable from underwriting activities
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	$ 23.0	$ 16.2	$ 5.2
Charged to Costs and Expenses	11.0	6.8	11.0
Charged to Other Accounts	0.0	0.0	0.0
Deductions	0.0	0.0	0.0
Balance at End of Year	34.0	23.0	16.2
Reinsurance
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	0.0	0.0	0.0
Charged to Costs and Expenses	0.0
Charged to Other Accounts	0.0	0.0	0.0
Deductions	0.0	0.0	0.0
Balance at End of Year	$ 0.0	$ 0.0	$ 0.0

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

No definition available.

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- Definition

Amount of valuation and qualifying accounts and reserves.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 4
-Subparagraph (SX 210.12-09)
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24092-122690

+ Details

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- Definition

Amount of increase in valuation and qualifying accounts and reserves from charge to cost and expense.

+ References

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- Definition

Amount of increase in valuation and qualifying accounts and reserves from charge to accounts other than cost and expense.

+ References

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- Definition

Amount of decrease in valuation and qualifying accounts and reserves.

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