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, 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 income	67.0	48.0	13.2								67.0	48.0	13.2
Dividend reinvestment plan	2.3							2.3
Dividend reinvestment plan (in shares)				28,764
Stock-based compensation costs	1.6							1.6
Stock issued under stock-based compensation plans				$ 0.1				(0.1)
Stock issued under stock-based compensation (in shares)				99,126
Employees’ tax withholding for stock-based compensation	(2.9)							(2.9)
Employee's tax withholding for stock-based compensation (in shares)				(37,945)
Temporary equity adjustment to redemption value	(0.1)										(0.1)
Dividends declared on common stock	(31.9)	(11.3)	(6.0)								(31.9)	(11.3)	(6.0)
Dividends declared on preferred stock	(7.4)										(7.4)
Other comprehensive income (loss), net of tax	14.4	0.1												14.4		0.1
BALANCE at Dec. 31, 2019	2,586.0	1,376.1	837.2	$ 51.1	$ 0.1		242.0	1,506.7	765.0	370.9	803.1	613.3	466.3	(16.9)		(2.3)
BALANCE (in shares) at Dec. 31, 2019				51,063,460	24,577	1,972,052
BALANCE at Sep. 30, 2020	2,522.3	1,435.1	851.7	$ 51.6	$ 0.1		242.0	1,549.2	765.0	350.9	720.7	672.9	500.8	(41.2)		(2.9)
BALANCE (in shares) at Sep. 30, 2020				51,611,789	24,577	1,972,052
Stockholders' Equity Rollforward
Net income	88.9	56.6	13.7								88.9	56.6	13.7
Dividend reinvestment plan	0.4							0.4
Dividend reinvestment plan (in shares)				6,698
Stock-based compensation costs	1.4							1.4
Stock issued under stock-based compensation plans				$ 0.1				(0.1)
Stock issued under stock-based compensation (in shares)				55,161
Employees’ tax withholding for stock-based compensation	(0.9)							(0.9)
Employee's tax withholding for stock-based compensation (in shares)				(14,175)
Temporary equity adjustment to redemption value	(0.9)										(0.9)
Return of capital to Spire			(11.0)							(11.0)
Dividends declared on common stock	(33.8)		(5.5)								(33.8)		(5.5)
Dividends declared on preferred stock	(3.7)										(3.7)
Other comprehensive income (loss), net of tax	13.1	0.1												13.1		0.1
BALANCE at Dec. 31, 2020	$ 2,586.8	$ 1,491.8	$ 848.9	$ 51.7	$ 0.1		$ 242.0	$ 1,550.0	$ 765.0	$ 339.9	$ 771.2	$ 729.5	$ 509.0	$ (28.1)		$ (2.8)
BALANCE (in shares) at Dec. 31, 2020				51,659,473	24,577	1,972,052

[1] Accumulated other comprehensive income (loss)