Document and Entity Information
Oct. 09, 2020
Document and Entity Information [Abstract]  
Document Type 8-K
Document Period End Date Oct. 09, 2020
Entity Registrant Name Arch Capital Group Ltd.
Entity Incorporation, State or Country Code D0
Entity Tax Identification Number 98-0374481
Entity Address, Address Line One Waterloo House, Ground Floor
Entity Address, Address Line Two 100 Pitts Bay Road
Entity Address, City or Town Pembroke
Entity Address, Postal Zip Code HM 08
Entity Address, Country BM
City Area Code 441
Local Phone Number 278-9250
Written Communications false
Soliciting Material false
Pre-commencement Tender Offer false
Pre-commencement Issuer Tender Offer false
Entity Listings [Line Items]  
Entity Emerging Growth Company false
Entity Central Index Key 0000947484
Amendment Flag false
Entity File Number 001-16209
Common shares  
Entity Listings [Line Items]  
Title of 12(b) Security Common shares, $0.0011 par value per share
Trading Symbol ACGL
Security Exchange Name NASDAQ
Depositary Series E Preferred Shares  
Entity Listings [Line Items]  
Title of 12(b) Security Depositary shares, each representing a 1/1,000th interest in a 5.25% Series E preferred share
Trading Symbol ACGLP
Security Exchange Name NASDAQ
Depositary Series F Preferred Shares  
Entity Listings [Line Items]  
Title of 12(b) Security Depositary shares, each representing a 1/1,000th interest in a 5.45% Series F preferred share
Trading Symbol ACGLO
Security Exchange Name NASDAQ