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Summary of Significant Accounting Policies (Reportable Segments and Discontinued Operations and Assets and Liabilities Held for Sale) (Details) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
	Apr. 04, 2019	Dec. 31, 2019	Dec. 31, 2017	Apr. 03, 2019	Dec. 31, 2018	May 11, 2018	Feb. 05, 2018	Dec. 31, 2012
Basis of Presentation
Percentage of par value of policy reinsured		15.00%
Payments to acquire business, net	$ 81.4
HG Global
Basis of Presentation
Surplus notes								$ 503.0
Preferred stocks \| HG Global
Basis of Presentation
Ownership interest (as a percent)		96.90%			96.90%
Fully diluted ownership interest (as a percent)		88.40%			85.00%
Common Stock \| HG Global
Basis of Presentation
Ownership interest (as a percent)		88.40%			88.40%
NSM Insurance HoldCo, LLC
Basis of Presentation
Ownership interest (as a percent)		96.40%			95.50%	95.00%
Fully diluted ownership interest (as a percent)		88.40%			85.00%	83.60%
Kudu
Basis of Presentation
Ownership interest (as a percent)	99.10%			49.50%			49.50%
Fully diluted ownership interest (as a percent)	85.40%			42.70%			42.70%
Increase in capital commitment		$ 100.0
Funded capital commitment	$ 250.0	350.0
Unfunded capital commitment		129.0
Series A BAM Surplus Note \| HG Global
Basis of Presentation
Surplus notes								203.0
Series B BAM Surplus Note \| HG Global
Basis of Presentation
Surplus notes								$ 300.0
Sirius Group, Tranzact, and Star and Shield \| Discontinued Operations, Held-for-sale \| Connecticut
Basis of Presentation
Other expenses			$ 3.7
Assets held for sale		3.0			$ 3.3
Delayed Draw Term Loans \| Kudu Debt \| Kudu
Basis of Presentation
Total commitment under revolving credit facility		125.0
Undrawn amount on facility		$ 68.0