Stockholders' Equity (Detail) $ / shares in Units, shares in Millions, $ in Millions				3 Months Ended
	Mar. 15, 2024 USD ($)	Feb. 20, 2024 USD ($) $ / shares shares	Feb. 08, 2024 $ / shares	Mar. 31, 2024 USD ($) $ / shares	Mar. 31, 2023 USD ($)	Dec. 31, 2023 $ / shares	Feb. 15, 2023
Class of Stock [Line Items]
Preferred shares par value (in dollars per share)				$ 1.00		$ 1.00
Liquidation preference (in dollars per share)				$ 25,000		$ 25,000
Fractional interest per one preference share			0.001				0.001
Depositary shares, dividends per share (in dollars per share)			$ 0.43750
Dividends paid | $				$ 2.6	$ 2.6
Argo Group International Holdings, Inc. | Brookfield Reinsurance
Class of Stock [Line Items]
Number of shares purchased (in shares) | shares		100.0
Share price (in dollars per share)		$ 1.00
Consideration transferred, equity interests issued | $		$ 100.0
Series A Preferred Stock
Class of Stock [Line Items]
Preferred stock, dividends declared (in dollars per share)			$ 437.50
Preferred stock, dividend rate (in percentage)			7.00%
Preferred shares par value (in dollars per share)			$ 1.00
Liquidation preference (in dollars per share)			$ 25,000
Dividends paid | $	$ 2.6