Schedule II Condensed Financial Information of Registrant - Schedule of Statements of Cash Flows (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Cash flows provided by (used in) operating activities:
Net income (loss)	$ (175.2)	$ 6.7	$ (54.1)
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Amortization and depreciation	18.5	43.4	33.2
Share-based payments expense	9.6	8.0	8.7
Loss on disposals of long-lived assets, net	0.6	23.3	5.5
Change in:
Accrued underwriting expenses and other liabilities	14.7	3.0	(43.7)
Other, net	0.0	17.9	9.8
Net cash flows from operating activities	53.2	99.7	71.9
Cash flows provided by (used in) investing activities:
Change in short-term investments	26.1	(116.4)	285.4
Settlements of foreign currency exchange forward contracts	(22.0)	(1.2)	9.4
Proceeds from business divestitures, net of cash transferred	14.9	0.0	28.3
Cash used in investing activities	(26.6)	(55.9)	(24.3)
Cash flows provided by (used in) financing activities:
Issuance of preferred shares, net of issuance costs	0.0	0.0	144.0
Activity under stock incentive plans	1.8	1.3	1.8
Payment of cash dividends to preferred shareholders	(10.5)	(10.5)	(4.6)
Payment of cash dividends to common shareholders	(43.4)	(43.7)	(43.0)
Cash used in financing activities	(52.1)	(52.9)	(26.8)
Change in cash	(25.1)	(2.7)	11.0
Cash, beginning of year	146.1
Cash, end of period	50.2	146.1
Argo Group International Holdings, Ltd (Parent  Guarantor)
Cash flows provided by (used in) operating activities:
Net income (loss)	(175.2)	6.7	(54.1)
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Amortization and depreciation	1.5	1.5	1.1
Share-based payments expense	2.8	2.3	3.6
Net realized investment and other losses (gains)	0.0	0.0	8.3
Loss on disposals of long-lived assets, net	(3.5)	(3.0)	0.1
Undistributed earnings of subsidiaries	148.0	(14.3)	17.4
Change in:
Prepaid assets	(1.8)	7.2	(2.2)
Accrued underwriting expenses and other liabilities	6.0	(4.1)	(9.1)
Due to subsidiaries	28.8	(12.1)	(11.1)
Other, net	4.7	(3.9)	(7.8)
Net cash flows from operating activities	11.3	(19.7)	(53.8)
Cash flows provided by (used in) investing activities:
Change in short-term investments	12.7	(13.9)	0.0
Settlements of foreign currency exchange forward contracts	(2.0)	0.5	0.1
Capital contribution to subsidiaries	0.0	0.0	(145.3)
Proceeds from business divestitures, net of cash transferred	0.0	0.0	30.0
Dividend received from subsidiaries	33.3	85.0	71.9
Cash used in investing activities	44.0	71.6	(43.3)
Cash flows provided by (used in) financing activities:
Issuance of preferred shares, net of issuance costs	0.0	0.0	144.0
Activity under stock incentive plans	1.8	1.3	1.8
Payment of cash dividends to preferred shareholders	(10.5)	(10.5)	(4.6)
Payment of cash dividends to common shareholders	(43.4)	(43.7)	(43.0)
Cash used in financing activities	(52.1)	(52.9)	98.2
Change in cash	3.2	(1.0)	1.1
Cash, beginning of year	2.0	3.0	1.9
Cash, end of period	$ 5.2	$ 2.0	$ 3.0