v3.26.1
Investments - Schedule of Fair Value Measurements (Details) - EBP 009 - USD ($)
Dec. 31, 2025
Dec. 31, 2024
EBP, Investment, Fair Value and NAV [Line Items]    
Total Assets in the Fair Value Hierarchy $ 760,079,577 $ 672,735,977
Total Assets 760,079,577 672,735,977
Fair Value Measured at Net Asset Value Per Share    
EBP, Investment, Fair Value and NAV [Line Items]    
Total Assets in the Fair Value Hierarchy [1] 10,143,686 12,908,694
Level 1    
EBP, Investment, Fair Value and NAV [Line Items]    
Total Assets in the Fair Value Hierarchy 192,609,966 176,257,602
Level 2    
EBP, Investment, Fair Value and NAV [Line Items]    
Total Assets in the Fair Value Hierarchy 557,325,925 483,569,681
Fair Value Hierarchy    
EBP, Investment, Fair Value and NAV [Line Items]    
Total Assets in the Fair Value Hierarchy 749,935,891 659,827,283
Mutual Funds    
EBP, Investment, Fair Value and NAV [Line Items]    
Total Assets in the Fair Value Hierarchy 128,245,413 120,039,325
Mutual Funds | Level 1    
EBP, Investment, Fair Value and NAV [Line Items]    
Total Assets in the Fair Value Hierarchy 128,245,413 120,039,325
Common / Collective Trusts    
EBP, Investment, Fair Value and NAV [Line Items]    
Total Assets in the Fair Value Hierarchy 557,325,925 483,569,681
Common / Collective Trusts | Level 2    
EBP, Investment, Fair Value and NAV [Line Items]    
Total Assets in the Fair Value Hierarchy 557,325,925 483,569,681
Spire Inc. ESOP    
EBP, Investment, Fair Value and NAV [Line Items]    
Total Assets in the Fair Value Hierarchy 54,835,856 49,373,212
Spire Inc. ESOP | Level 1    
EBP, Investment, Fair Value and NAV [Line Items]    
Total Assets in the Fair Value Hierarchy 54,835,856 49,373,212
Self-Directed Brokerage Accounts    
EBP, Investment, Fair Value and NAV [Line Items]    
Total Assets in the Fair Value Hierarchy 9,528,697 6,845,065
Self-Directed Brokerage Accounts | Level 1    
EBP, Investment, Fair Value and NAV [Line Items]    
Total Assets in the Fair Value Hierarchy $ 9,528,697 $ 6,845,065
[1] Certain investments that are measured at fair value using the NAV per share (or its equivalent) as a practical expedient have not been categorized in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the amounts presented on the Statements of Net Assets Available for Benefits.