Schedule II Condensed Financial Information of Registrant - Schedule of Balance Sheets (Detail) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Assets
Cash	$ 50.2	$ 146.1
Operating lease right-of-use assets	57.7	81.4
Other assets	121.5	211.6
Total assets	10,034.4	10,317.8
Liabilities and Shareholders' Equity
Junior subordinated debentures	258.6	258.2
Accrued underwriting expenses and other liabilities	121.3	166.6
Operating lease liabilities	66.4	97.7
Total liabilities	8,801.5	8,582.6
Shareholders' equity	1,232.9	1,735.2	$ 1,857.8	$ 1,763.7
Total liabilities and shareholders' equity	10,034.4	10,317.8
Argo Group International Holdings, Ltd (Parent  Guarantor)
Assets
Short-term investments	1.8	14.5
Investment in subsidiaries	1,281.7	1,740.8
Cash	5.2	2.0	$ 3.0	$ 1.9
Operating lease right-of-use assets	4.6	5.3
Other assets	6.7	5.2
Total assets	1,300.0	1,767.8
Liabilities and Shareholders' Equity
Junior subordinated debentures	28.4	28.4
Accrued underwriting expenses and other liabilities	10.0	3.6
Operating lease liabilities	4.6	5.3
Due to subsidiaries	14.0	(4.7)
Intercompany notes payable	10.1	0.0
Total liabilities	67.1	32.6
Shareholders' equity	1,232.9	1,735.2
Total liabilities and shareholders' equity	$ 1,300.0	$ 1,767.8