CONDENSED CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY (UNAUDITED) - USD ($) $ in Millions	Total	Spire Missouri	Spire Alabama	Common Stock	Common Stock Spire Missouri	Common Stock Spire Alabama	Preferred Stock	Paid-in Capital	Paid-in Capital Spire Missouri	Paid-in Capital Spire Alabama	Retained Earnings	Retained Earnings Spire Missouri	Retained Earnings Spire Alabama	AOCI	[1]	AOCI Spire Missouri	[1]
BALANCE at Sep. 30, 2018	$ 2,255.4	$ 1,259.9	$ 808.7	$ 50.7	$ 0.1			$ 1,482.7	$ 760.3	$ 390.9	$ 715.6	$ 501.1	$ 417.8	$ 6.4		$ (1.6)
BALANCE (in shares) at Sep. 30, 2018				50,671,903	24,577	1,972,052
Stockholders' Equity Rollforward
Net (Loss) Income	218.9	132.3	72.6								218.9	132.3	72.6
Preferred stock offering	242.0						$ 242.0
Common stock issued	4.5			$ 0.1				4.4
Common stock issued (in shares)				59,630
Dividend reinvestment plan	1.2							1.2
Dividend reinvestment plan (in shares)				15,771
Stock-based compensation costs	6.7	3.5						6.7	3.5
Stock issued under stock-based compensation plans				$ 0.1				(0.1)
Stock issued under stock-based compensation (in shares)				86,328
Employees’ tax withholding for stock-based compensation	(2.3)			$ (0.1)				(2.2)
Employee's tax withholding for stock-based compensation (in shares)				(28,001)
Return of capital to Spire			(20.0)							(20.0)
Dividends declared on common stock	(90.2)	(19.5)	(17.0)								(90.2)	(19.5)	(17.0)
Other comprehensive income (loss), net of tax	(23.6)	0.1												(23.6)		0.1
BALANCE at Jun. 30, 2019	2,612.6	1,376.3	844.3	$ 50.8	$ 0.1		242.0	1,492.7	763.8	370.9	844.3	613.9	473.4	(17.2)		(1.5)
BALANCE (in shares) at Jun. 30, 2019				50,805,631	24,577	1,972,052
BALANCE at Mar. 31, 2019	2,406.0	1,374.0	838.7	$ 50.7	$ 0.1			1,485.6	762.7	370.9	877.5	612.8	467.8	(7.8)		(1.6)
BALANCE (in shares) at Mar. 31, 2019				50,742,637	24,577	1,972,052
Stockholders' Equity Rollforward
Net (Loss) Income	(3.0)	1.1	5.6								(3.0)	1.1	5.6
Preferred stock offering	242.0						242.0
Common stock issued	4.5			$ 0.1				4.4
Common stock issued (in shares)				59,630
Dividend reinvestment plan	0.4							0.4
Dividend reinvestment plan (in shares)				4,504
Stock-based compensation costs	2.3	1.1						2.3	1.1
Stock issued under stock-based compensation (in shares)				(1,140)
Dividends declared on common stock	(30.2)										(30.2)
Other comprehensive income (loss), net of tax	(9.4)	0.1												(9.4)		0.1
BALANCE at Jun. 30, 2019	2,612.6	1,376.3	844.3	$ 50.8	$ 0.1		242.0	1,492.7	763.8	370.9	844.3	613.9	473.4	(17.2)		(1.5)
BALANCE (in shares) at Jun. 30, 2019				50,805,631	24,577	1,972,052
BALANCE at Sep. 30, 2019	2,543.0	1,339.3	830.0	$ 51.0	$ 0.1		242.0	1,505.8	765.0	370.9	775.5	576.6	459.1	(31.3)		(2.4)
BALANCE (in shares) at Sep. 30, 2019				50,973,515	24,577	1,972,052
Stockholders' Equity Rollforward
Net (Loss) Income	108.3	129.0	74.6								108.3	129.0	74.6
Common stock issued	24.6			$ 0.3				24.3
Common stock issued (in shares)				321,232
Dividend reinvestment plan	8.7			$ 0.1				8.6
Dividend reinvestment plan (in shares)				114,851
Stock-based compensation costs	4.5							4.5
Stock issued under stock-based compensation plans				$ 0.1				(0.1)
Stock issued under stock-based compensation (in shares)				108,522
Employees’ tax withholding for stock-based compensation	(3.2)							(3.2)
Employee's tax withholding for stock-based compensation (in shares)				(40,288)
Temporary equity adjustment to redemption value	1.7										1.7
Return of capital to Spire			(20.0)							(20.0)
Dividends declared on common stock	(96.1)	(33.9)	(18.0)								(96.1)	(33.9)	(18.0)
Dividends declared on preferred stock	(14.8)										(14.8)
Other comprehensive income (loss), net of tax	(18.3)													(18.3)
BALANCE at Jun. 30, 2020	2,558.4	1,434.4	866.6	$ 51.5	$ 0.1		242.0	1,539.9	765.0	350.9	774.6	671.7	515.7	(49.6)		(2.4)
BALANCE (in shares) at Jun. 30, 2020				51,477,832	24,577	1,972,052
BALANCE at Mar. 31, 2020	2,665.6	1,439.1	869.0	$ 51.2	$ 0.1		242.0	1,520.7	765.0	350.9	902.3	676.5	518.1	(50.6)		(2.5)
BALANCE (in shares) at Mar. 31, 2020				51,229,061	24,577	1,972,052
Stockholders' Equity Rollforward
Net (Loss) Income	(92.3)	6.5	3.6								(92.3)	6.5	3.6
Common stock issued	15.1			$ 0.2				14.9
Common stock issued (in shares)				208,474
Dividend reinvestment plan	3.1			$ 0.1				3.0
Dividend reinvestment plan (in shares)				40,968
Stock-based compensation costs	1.4							1.4
Stock issued under stock-based compensation (in shares)				(230)
Employees’ tax withholding for stock-based compensation	(0.1)							(0.1)
Employee's tax withholding for stock-based compensation (in shares)				(441)
Temporary equity adjustment to redemption value	0.6										0.6
Dividends declared on common stock	(32.3)	(11.3)	(6.0)								(32.3)	(11.3)	(6.0)
Dividends declared on preferred stock	(3.7)										(3.7)
Other comprehensive income (loss), net of tax	1.0	0.1												1.0		0.1
BALANCE at Jun. 30, 2020	$ 2,558.4	$ 1,434.4	$ 866.6	$ 51.5	$ 0.1		$ 242.0	$ 1,539.9	$ 765.0	$ 350.9	$ 774.6	$ 671.7	$ 515.7	$ (49.6)		$ (2.4)
BALANCE (in shares) at Jun. 30, 2020				51,477,832	24,577	1,972,052

[1] Accumulated other comprehensive income (loss)