CONDENSED CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY (UNAUDITED) - USD ($) $ in Millions	Total	Spire Missouri	Spire Alabama	Common Stock Outstanding	Common Stock Outstanding Spire Missouri	Common Stock Outstanding 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, 2017	$ 1,991.3	$ 1,171.0	$ 867.4	$ 48.3	$ 0.1			$ 1,325.6	$ 756.1	$ 420.9	$ 614.2	$ 416.5	$ 446.5	$ 3.2		$ (1.7)
BALANCE (in shares) at Sep. 30, 2017				48,263,243	24,577	1,972,052
Stockholders' Equity Rollforward
Net income (loss)	240.1	139.3	12.3								240.1	139.3	12.3
Return of capital to Spire			(30.0)							(30.0)
Common stock offering	153.0			$ 2.3				150.7
Common stock offering (in shares)				2,300,000
Dividend reinvestment plan	1.2							1.2
Dividend reinvestment plan (in shares)				16,952
Stock-based compensation costs	5.6	3.1						5.6	3.1
Stock issued under stock-based compensation plans				$ 0.1				(0.1)
Stock issued under stock-based compensation plans (in shares)				111,742
Employees’ tax withholding for stock-based compensation	(2.8)							(2.8)
Employee's tax withholding for stock-based compensation (in shares)				(33,777)
Dividends declared on common stock	(81.9)	(36.0)	(22.5)								(81.9)	(36.0)	(22.5)
Other comprehensive income/loss, net of tax	1.2													1.2
BALANCE at Jun. 30, 2018	2,307.7	1,277.4	827.2	$ 50.7	$ 0.1			1,480.2	759.2	390.9	772.4	519.8	436.3	4.4		(1.7)
BALANCE (in shares) at Jun. 30, 2018				50,658,160	24,577	1,972,052
BALANCE at Mar. 31, 2018	2,153.5	1,273.9	828.4	$ 48.4	$ 0.1			1,327.3	758.3	390.9	773.7	517.3	437.5	4.1		(1.8)
BALANCE (in shares) at Mar. 31, 2018				48,354,779	24,577	1,972,052
Stockholders' Equity Rollforward
Net income (loss)	25.9	11.5	6.3								25.9	11.5	6.3
Common stock offering	153.0			$ 2.3				150.7
Common stock offering (in shares)				2,300,000
Dividend reinvestment plan	0.4							0.4
Dividend reinvestment plan (in shares)				5,949
Stock-based compensation costs	1.8	0.9						1.8	0.9
Stock issued under stock-based compensation plans (in shares)				(2,372)
Employee's tax withholding for stock-based compensation (in shares)				(196)
Dividends declared on common stock	(27.2)	(9.0)	(7.5)								(27.2)	(9.0)	(7.5)
Other comprehensive income/loss, net of tax	0.3	0.1												0.3		0.1
BALANCE at Jun. 30, 2018	2,307.7	1,277.4	827.2	$ 50.7	$ 0.1			1,480.2	759.2	390.9	772.4	519.8	436.3	4.4		(1.7)
BALANCE (in shares) at Jun. 30, 2018				50,658,160	24,577	1,972,052
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 income (loss)	218.9	132.3	72.6								218.9	132.3	72.6
Return of capital to Spire			(20.0)							(20.0)
Preferred stock offering	242.0						$ 242.0
Common stock offering	4.5			$ 0.1				4.4
Common stock offering (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 plans (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)
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 income (loss)	(3.0)	1.1	5.6								(3.0)	1.1	5.6
Preferred stock offering	242.0						242.0
Common stock offering	4.5			$ 0.1				4.4
Common stock offering (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 plans (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

[1] Accumulated other comprehensive income (loss)