XML 61 R48.htm IDEA: XBRL DOCUMENT v3.22.1
Pension Plans and Other Postretirement Benefits - Additional Information (Details)
3 Months Ended 6 Months Ended
Dec. 23, 2021
USD ($)
Dec. 22, 2021
USD ($)
Mar. 31, 2022
USD ($)
plan
Mar. 31, 2022
USD ($)
plan
Sep. 30, 2021
USD ($)
Mar. 31, 2021
USD ($)
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]            
Settlement benefits paid       $ 0    
Regulatory assets     $ 1,270,800,000 $ 1,270,800,000 $ 1,300,000,000.0 $ 1,194,000,000.0
Remaining recovery period for regulatory assets for which no return on investment during recovery period is provided (in years)     15 years      
Medical insurance available until age is reached after early retirement       65 years    
Recovery in rates for postretirement benefit $ 8,600,000          
Spire Missouri            
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]            
Regulatory assets     $ 685,400,000 $ 685,400,000 759,400,000 641,800,000
Spire Alabama            
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]            
Regulatory assets     $ 547,700,000 547,700,000 $ 502,100,000 $ 513,000,000.0
Spire Missouri West | Pension Cost | MoPSC | Infrastructure System Replacement Surcharge            
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]            
Regulatory assets 4,400,000 $ 5,500,000        
Spire Missouri West | Pension and Other Postretirement Benefits            
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]            
Amortization of assets $ 1,100,000 3,300,000        
Remaining recovery period for regulatory assets for which no return on investment during recovery period is provided (in years) 8 years          
Additional remaining recovery period for regulatory assets for which no return on investment during recovery period is provided 8 years          
Spire Missouri East | Pension Cost | MoPSC | Infrastructure System Replacement Surcharge            
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]            
Regulatory assets $ 32,400,000 29,000,000.0        
Spire Missouri East | Pension and Other Postretirement Benefits            
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]            
Amortization of assets $ 11,000,000.0 $ 21,600,000        
Remaining recovery period for regulatory assets for which no return on investment during recovery period is provided (in years) 8 years          
Additional remaining recovery period for regulatory assets for which no return on investment during recovery period is provided 8 years          
Other Postretirement Benefits Plan            
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]            
Employer contributions       $ 10,000,000.0    
Other Postretirement Benefits Plan | Spire Missouri            
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]            
Number of Plans | plan     1 1    
Settlement benefits paid     $ 21,600,000 $ 21,600,000    
Settlement loss     $ 6,800,000 $ 6,800,000    
Discount rates     3.60% 3.60% 3.00%  
Anticipated contributions to pension plans for qualified trust       $ 16,500,000    
Other Postretirement Benefits Plan | Spire Missouri | Qualified Plan            
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]            
Employer contributions       21,200,000    
Other Postretirement Benefits Plan | Spire Missouri | Nonqualified Plan            
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]            
Employer contributions       $ 0    
Other Postretirement Benefits Plan | Spire Alabama            
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]            
Number of Plans | plan     2 2    
Settlement benefits paid     $ 17,400,000 $ 17,400,000    
Settlement loss     $ 4,900,000 4,900,000    
Anticipated contributions to pension plans for qualified trust       $ 4,400,000    
Other Postretirement Benefits Plan | Spire Alabama First Plan            
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]            
Discount rates     3.60% 3.60% 3.00%  
Settlement losses amortized over remaining actuarial life       12 years 3 months 18 days    
Other Postretirement Benefits Plan | Spire Alabama Second Plan            
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]            
Discount rates         3.10%  
Settlement losses amortized over remaining actuarial life       12 years 7 months 6 days    
Other Postretirement Benefits Plan | Spire Missouri            
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]            
Employer contributions       $ 0    
Anticipated contributions to pension plans for qualified trust       0    
Other Postretirement Benefits Plan | Spire Alabama            
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]            
Employer contributions       0    
Anticipated contributions to pension plans for qualified trust       $ 0