Schedule II Condensed Financial Information of Registrant - Schedule of Statements of Income (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Revenue:
Net investment expense	$ 129.8	$ 187.6	$ 112.7
Net investment and other (gains) losses	(115.3)	32.6	(3.6)
Total revenue	1,754.9	2,130.3	1,889.6
Expenses:
Interest expense	26.8	21.6	26.9
Non-operating expenses	51.5	43.7	21.1
Total expenses	1,938.1	2,125.0	1,936.0
Net income (loss)	(175.2)	6.7	(54.1)
Dividends on preferred shares	10.5	10.5	4.6
Net income (loss) attributable to common shareholders, basic	(185.7)	(3.8)	(58.7)
Argo Group International Holdings, Ltd (Parent  Guarantor)
Revenue:
Net investment expense	0.0	0.0	0.0
Net investment and other (gains) losses	0.0	0.0	(8.3)
Total revenue	0.0	0.0	(8.3)
Expenses:
Interest expense	1.6	1.2	3.6
Operating expenses	(0.6)	6.2	20.4
Non-operating expenses	26.2	0.2	4.4
Total expenses	27.2	7.6	28.4
Net income before equity in earnings of subsidiaries	(27.2)	(7.6)	(36.7)
Equity in undistributed earnings of subsidiaries	(148.0)	14.3	(17.4)
Net income (loss)	(175.2)	6.7	(54.1)
Dividends on preferred shares	10.5	10.5	4.6
Net income (loss) attributable to common shareholders, basic	$ (185.7)	$ (3.8)	$ (58.7)