XML 114 R100.htm IDEA: XBRL DOCUMENT
v3.8.0.1

Commitments, Contingencies and Off-Balance Sheet Arrangements - Litigation, Regulatory and Taxation Matters- Additional Information (Detail) | 12 Months Ended
--- | ---
Dec. 31, 2017 Companies
Minimum [Member] |
Commitments Contingencies And Off Balance Sheet Arrangements [Line Items] |
Number of micro-captive insurance companies organized or managed | 100

X
- Definition Commitments Contingencies And Off Balance Sheet Arrangements [Line Items] + References No definition available. + Details
Name: | ajg_CommitmentsContingenciesAndOffBalanceSheetArrangementsLineItems
Namespace Prefix: | ajg_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Micro captive Insurance Companies Managed + References No definition available. + Details
Name: | ajg_MicroCaptiveInsuranceCompaniesManaged
Namespace Prefix: | ajg_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |