XML 12 R1.htm IDEA: XBRL DOCUMENT v3.25.2
Cover Page
shares in Millions
 6 Months Ended
Jun. 30, 2025
shares
Cover [Abstract]  
Document Type 10-Q
Document Quarterly Report true
Document Period End Date Jun. 30, 2025
Document Transition Report false
Entity File Number 1-09761
Entity Registrant Name ARTHUR J. GALLAGHER & CO.
Entity Incorporation, State or Country Code DE
Entity Tax Identification Number 36-2151613
Entity Address, Address Line One 2850 Golf Road
Entity Address, City or Town Rolling Meadows
Entity Address, State or Province IL
Entity Address, Postal Zip Code 60008
City Area Code 630
Local Phone Number 773-3800
Title of 12(b) Security Common Stock, par value $1.00 per share
Trading Symbol AJG
Security Exchange Name NYSE
Entity Current Reporting Status Yes
Entity Interactive Data Current Yes
Entity Filer Category Large Accelerated Filer
Entity Small Business false
Entity Emerging Growth Company false
Entity Shell Company false
Entity Common Stock, Shares Outstanding 256.4
Entity Central Index Key 0000354190
Current Fiscal Year End Date --12-31
Document Fiscal Year Focus 2025
Document Fiscal Period Focus Q2
Amendment Flag false