Share Transactions	6 Months Ended
Jun. 30, 2026
Stockholders' Equity Note [Abstract]
Share transactions	Share Repurchases The Board of Directors of Arch Capital has authorized the investment in Arch Capital’s common shares through a share repurchase program. Since the inception of the share repurchase program, Arch Capital has repurchased 475.7 million common shares for an aggregate purchase price of $9.7 billion. For the six months ended June 30, 2026, Arch Capital repurchased 20.7 million common shares under the share repurchase program with an aggregate purchase price of approximately $1.9 billion. Arch Capital repurchased 4.1 million common shares under the share repurchase program with an aggregate purchase price of approximately $359.7 million during the six months ended June 30, 2025. At June 30, 2026, $2.2 billion of share repurchases were available under the program. On April 19, 2026, the Company increased its authorization for its existing share repurchase program by $3.0 billion, which, as in the past, may be effected from time to time in open market or privately negotiated transactions. The timing and amount of the repurchase transactions under this program will depend on a variety of factors, including market conditions and corporate and regulatory considerations.

Share Transactions

6 Months Ended

Jun. 30, 2026

Stockholders' Equity Note [Abstract]

Share Repurchases

The Board of Directors of Arch Capital has authorized the investment in Arch Capital’s common shares through a share repurchase program. Since the inception of the share repurchase program, Arch Capital has repurchased 475.7 million common shares for an aggregate purchase price of $9.7 billion. For the six months ended June 30, 2026, Arch Capital repurchased 20.7 million common shares under the share repurchase program with an aggregate purchase price of approximately $1.9 billion. Arch Capital repurchased 4.1 million common shares under the share repurchase program with an aggregate purchase price of approximately $359.7 million during the six months ended June 30, 2025. At June 30, 2026, $2.2 billion of share repurchases were available under the program.

On April 19, 2026, the Company increased its authorization for its existing share repurchase program by $3.0 billion, which, as in the past, may be effected from time to time in open market or privately negotiated transactions. The timing and amount of the repurchase transactions under this program will depend on a variety of factors, including market conditions and corporate and regulatory considerations.