Statutory Financial Information (Narrative) (Details) $ in Millions	Dec. 31, 2019 USD ($)
Statutory Accounting Practices [Line Items]
Amount of cash and investments held as funds at Lloyd's	$ 899.3
Funds at Lloyd's, holding company	336.7
United States [Member]
Statutory Accounting Practices [Line Items]
Amount available for dividend payment	561.8
Bermuda [Member]
Statutory Accounting Practices [Line Items]
Amount available for dividend payment	$ 401.0