Shareholders' Equity (Tables)

12 Months Ended

Sep. 30, 2020

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, 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	)
Other comprehensive loss		(9.4	)		(0.5	)		—		(9.9	)
Balance at September 30, 2020	$	(38.4	)	$	(2.9	)	$	0.1	$	(41.2	)
Spire Missouri
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	)
Other comprehensive loss		—			(0.5	)		—		(0.5	)
Balance at September 30, 2020	$	—		$	(2.9	)	$	—	$	(2.9	)