v3.25.2
Cover - shares
 6 Months Ended
Jun. 30, 2025
Jul. 28, 2025
Entity Information [Line Items]    
Document Type 10-Q  
Document Quarterly Report true  
Document Period End Date Jun. 30, 2025  
Document Transition Report false  
Entity File Number 001-32550  
Entity Registrant Name WESTERN ALLIANCE BANCORPORATION  
Entity Incorporation, State or Country Code DE  
Entity Tax Identification Number 88-0365922  
Entity Address, Address Line One One E. Washington Street, Suite 1400  
Entity Address, City or Town Phoenix  
Entity Address, State or Province AZ  
Entity Address, Postal Zip Code 85004  
City Area Code 602  
Local Phone Number 389-3500  
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   110,368,816
Entity Central Index Key 0001212545  
Document Fiscal Year Focus 2025  
Document Fiscal Period Focus Q2  
Amendment Flag false  
Current Fiscal Year End Date --12-31  
Common Stock    
Entity Information [Line Items]    
Title of 12(b) Security Common Stock, $0.0001 Par Value  
Trading Symbol WAL  
Security Exchange Name NYSE  
Noncumulative Preferred Stock    
Entity Information [Line Items]    
Title of 12(b) Security Depositary Shares, Each Representing a 1/400th Interest in a Share of 4.250% Fixed-Rate Reset Non-Cumulative Perpetual Preferred Stock, Series A  
Trading Symbol WAL PrA  
Security Exchange Name NYSE