XML 123 R106.htm IDEA: XBRL DOCUMENT

Investments in Unconsolidated Affiliates (Carrying Values of Investments) (Details) - White Mountains - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Other Investments	$ 325.6	$ 208.8
Limited liability companies and private equity securities
Schedule of Equity Method Investments [Line Items]
Other Investments	138.1	58.0
Investments accounted for under the equity method
Schedule of Equity Method Investments [Line Items]
Other Investments	1.3	4.6
Investments In Unconsolidated Entities
Schedule of Equity Method Investments [Line Items]
Other Investments	139.4	62.6
Other unconsolidated investments
Schedule of Equity Method Investments [Line Items]
Other Investments	$ 186.2	$ 146.2