CONDENSED CONSOLIDATED BALANCE SHEETS (UNAUDITED) (Parenthetical) - USD ($) $ in Millions	Jun. 30, 2020	Sep. 30, 2019	Jun. 30, 2019
ASSETS
Non-utility property, accumulated depreciation and amortization	$ 20.8	$ 12.7	$ 11.1
Capitalization:
Preferred stock, par value (in dollars per share)	$ 25.00	$ 25.00	$ 25.00
Preferred stock, depositary shares authorized (in shares)	10,000,000.0	10,000,000.0	10,000,000.0
Preferred stock, depositary shares outstanding (in shares)	10,000,000.0	10,000,000.0	10,000,000.0
Preferred stock, depositary shares issued (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, authorized (in shares)	70,000,000.0	70,000,000.0	70,000,000.0
Common stock, issued (in shares)	51,500,000	51,000,000.0	50,800,000
Common stock, outstanding (in shares)	51,500,000	51,000,000.0	50,800,000
Spire Missouri
Capitalization:
Common stock, par value (in dollars per share)	$ 1.00	$ 1.00	$ 1.00
Common stock, authorized (in shares)	50,000,000.0	50,000,000.0	50,000,000.0
Common stock, issued (in shares)	24,577	24,577	24,577
Common stock, outstanding (in shares)	24,577	24,577	24,577
Spire Alabama
Capitalization:
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01	$ 0.01
Common stock, authorized (in shares)	3,000,000.0	3,000,000.0	3,000,000.0
Common stock, issued (in shares)	2,000,000.0	2,000,000.0	2,000,000.0
Common stock, outstanding (in shares)	2,000,000.0	2,000,000.0	2,000,000.0