Shareholders' Equity (Tables)

12 Months Ended

Sep. 30, 2019

Stockholders Equity Note [Abstract]

Schedule of Accumulated Other Comprehensive Income

The components of accumulated other comprehensive income (AOCI), net of income taxes, recognized in the balance sheets at September 30 were as follows:

	Net Unrealized Gains (Losses) on Cash Flow Hedges			Defined Benefit Pension and Other Postretirement Benefit Plans			Net Unrealized Losses on Available-for- Sale Debt Securities			Total
Spire
Balance at September 30, 2017	$	4.9		$	(1.5	)	$	(0.2	)	$	3.2
Other comprehensive income		2.0			0.3			0.2			2.5
Reclassification of certain income tax effects		1.0			(0.3	)		—			0.7
Balance at September 30, 2018		7.9			(1.5	)		—			6.4
Other comprehensive (loss) income		(36.9	)		(0.9	)		0.1			(37.7	)
Balance at September 30, 2019	$	(29.0	)	$	(2.4	)	$	0.1		$	(31.3	)
Spire Missouri
Balance at September 30, 2017	$	0.1		$	(1.6	)	$	(0.2	)	$	(1.7	)
Other comprehensive (loss) income		(0.1	)		0.3			0.2			0.4
Reclassification of certain income tax effects		—			(0.3	)		—			(0.3	)
Balance at September 30, 2018		—			(1.6	)		—			(1.6	)
Other comprehensive loss		—			(0.8	)		—			(0.8	)
Balance at September 30, 2019	$	—		$	(2.4	)	$	—		$	(2.4	)