Financing - Schedule of Variable Stock Purchase Contract Settlement Rates (Details) - Spire - Common Stock $1.00 par value	Feb. 28, 2021 $ / shares shares
Equity Units [Line Items]
Price divided by applicable market value to determine number of shares per stock purchase contract	$ 50.00
Maximum
Equity Units [Line Items]
Applicable market value per share	78.6906
Applicable market value per share, reference price	$ 64.24
Number of shares to be purchased per stock purchase contract, settlement rate | shares	0.7783
Minimum
Equity Units [Line Items]
Applicable market value per share, threshold appreciation price	$ 78.6906
Applicable market value per share	$ 64.24
Number of shares to be purchased per stock purchase contract, settlement rate | shares	0.6354