| DEI Document | Feb. 28, 2021 |
| Entity Information [Line Items] | |
| Entity Central Index Key | 0001212545 |
| Amendment Flag | false |
| Document Type | 8-K |
| Document Period End Date | Feb. 28, 2021 |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 001-32550 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Entity Tax Identification Number | 88-0365922 |
| Entity Registrant Name | WESTERN ALLIANCE BANCORPORATION |
| Entity Address, Address Line One | One E. Washington Street |
| 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 |
| Common Stock [Member] | |
| Entity Information [Line Items] | |
| Title of 12(b) Security | Common Stock, $0.0001 Par Value |
| Trading Symbol | WAL |
| Security Exchange Name | NYSE |
| Subordinated Debt [Member] | |
| Entity Information [Line Items] | |
| Title of 12(b) Security | 6.25% Subordinated Debentures due 2056 |
| Trading Symbol | WALA |
| Security Exchange Name | NYSE |
