Commitments and Contingencies (Details) $ in Millions	Jun. 30, 2017 USD ($)
Commitments and Contingencies Disclosure [Abstract]
Investment commitments	$ 1,560

Investment commitments primarily related to agreements entered into by the Company to invest in funds and separately managed accounts when called upon.

No definition available.

Name:	acgl_InvestmentCommitments
Namespace Prefix:	acgl_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant