v3.26.1
Cover Page - shares
 6 Months Ended
Jun. 30, 2026
Aug. 05, 2026
Document Information [Line Items]    
Document Type 10-Q  
Document Quarterly Report true  
Document Period End Date Jun. 30, 2026  
Document Transition Report false  
Entity File Number 001-13459  
Entity Registrant Name AFFILIATED MANAGERS GROUP, INC.  
Entity Incorporation, State or Country Code DE  
Entity Tax Identification Number 04-3218510  
Entity Address, Address Line One 1001 U.S. Highway One North  
Entity Address, City or Town Jupiter  
Entity Address, State or Province FL  
Entity Address, Postal Zip Code 33477  
City Area Code 800  
Local Phone Number 345-1100  
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   25,859,933
Entity Central Index Key 0001004434  
Amendment Flag false  
Current Fiscal Year End Date --12-31  
Document Fiscal Year Focus 2026  
Document Fiscal Period Focus Q2  
Common Stock ($0.01 par value)    
Document Information [Line Items]    
Title of 12(b) Security Common Stock ($0.01 par value)  
Trading Symbol AMG  
Security Exchange Name NYSE  
5.875% Junior Subordinated Notes due 2059    
Document Information [Line Items]    
Title of 12(b) Security 5.875% Junior Subordinated Notes due 2059  
Trading Symbol MGR  
Security Exchange Name NYSE  
4.750% Junior Subordinated Notes due 2060    
Document Information [Line Items]    
Title of 12(b) Security 4.750% Junior Subordinated Notes due 2060  
Trading Symbol MGRB  
Security Exchange Name NYSE  
4.200% Junior Subordinated Notes due 2061    
Document Information [Line Items]    
Title of 12(b) Security 4.200% Junior Subordinated Notes due 2061  
Trading Symbol MGRD  
Security Exchange Name NYSE  
6.750% Junior Subordinated Notes due 2064    
Document Information [Line Items]    
Title of 12(b) Security 6.750% Junior Subordinated Notes due 2064  
Trading Symbol MGRE  
Security Exchange Name NYSE