Selected Quarterly Financial Data (unaudited) Normalized Items (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
NetCasualtyGains [Line Items]
Revaluation of deferred tax liabilities	$ 0.0	$ 0.0	$ (9.4)
Canada Revenue Agency [Member]
NetCasualtyGains [Line Items]
Revaluation of deferred tax liabilities	0.7	$ 2.8	$ 0.0
United Kingdom [Member]
NetCasualtyGains [Line Items]
Revaluation of deferred tax liabilities	$ 12.3

Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations, attributable to increase (decrease) in the income tax rates.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 45
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=120406818&loc=d3e32059-109318

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32687-109319

Name:	us-gaap_IncomeTaxReconciliationChangeInEnactedTaxRate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration