Condensed Consolidated Balance Sheets (Current Period Unaudited) (Parentheticals) - USD ($) $ in Millions	Mar. 31, 2023	Sep. 30, 2022	Mar. 31, 2022
Non-utility property, accumulated depreciation and amortization	$ 60.6	$ 50.7	$ 41.3
Preferred stock, par value (in dollars per share)	$ 25.00	$ 25.00	$ 25.00
Common stock, par value (in dollars per share)	$ 1.00	$ 1.00	$ 1.00
Common stock, shares authorized (in shares)	70,000,000.0	70,000,000.0	70,000,000.0
Common stock, shares issued (in shares)	52,600,000	52,500,000	52,100,000
Common Stock, shares outstanding (in shares)	52,600,000	52,500,000	52,100,000
Depositary Shares [Member]
Preferred stock, shares authorized (in shares)	10,000,000.0	10,000,000.0	10,000,000.0
Preferred stock, shares issued (in shares)	10,000,000.0	10,000,000.0	10,000,000.0
Preferred stock, shares outstanding (in shares)	10,000,000.0	10,000,000.0	10,000,000.0
Spire Missouri [Member]
Common stock, par value (in dollars per share)	$ 1.00	$ 1.00	$ 1.00
Common stock, shares authorized (in shares)	50,000,000.0	50,000,000.0	50,000,000.0
Common stock, shares issued (in shares)	25,325	25,325	24,929
Common Stock, shares outstanding (in shares)	25,325	25,325	24,929
Spire Alabama Inc [Member]
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	3.0	3.0	3.0
Common stock, shares issued (in shares)	2.0	2.0	2.0
Common Stock, shares outstanding (in shares)	2.0	2.0	2.0