Condensed Consolidated Balance Sheets (Current Period Unaudited) (Parentheticals) - USD ($) $ in Millions	Jun. 30, 2022	Sep. 30, 2021	Jun. 30, 2021
Non-utility property, accumulated depreciation and amortization	$ 46.0	$ 32.1	$ 28.8
Preferred stock, par value (in dollars per share)	$ 25.00	$ 25.00	$ 25.00
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
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)	52,500,000	51,700,000	51,700,000
Common Stock, shares outstanding (in shares)	52,500,000	51,700,000	51,700,000
Spire Alabama Inc [Member]
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	3,000,000.0	3,000,000.0	3,000,000.0
Common stock, shares issued (in shares)	2,000,000.0	2,000,000.0	2,000,000.0
Common Stock, shares outstanding (in shares)	2,000,000.0	2,000,000.0	2,000,000.0
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	24,577	24,577
Common Stock, shares outstanding (in shares)	25,325	24,577	24,577