Subsequent Events (Details) - Subsequent Event - USD ($) $ in Millions	1 Months Ended
	Oct. 31, 2023	Oct. 25, 2023
Subsidiaries | Arch Re Bermuda | Letter Of Credit Facility
Subsequent Event [Line Items]
Maximum borrowing capacity		$ 530
Revolving credit agreement borrowings		$ 530
Variable Interest Entity, Primary Beneficiary | Bellemeade Re 2023-1 Ltd.
Subsequent Event [Line Items]
Excess of loss agreement, initial coverage at issuance	$ 233
Aggregate losses for new delinquencies, amount	$ 62
Excess of loss agreement, amortization period	10 years
Mortgage insurance-linked notes, amount	$ 187
Directly provided capacity, amount	$ 46