Note 2 - Revenue - Taxes Associated With Natural Gas Utility Services (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Gross Receipts Tax Amounts	$ 30.4	$ 21.9
Spire Missouri [Member]
Gross Receipts Tax Amounts	22.1	14.9
Spire Alabama Inc [Member]
Gross Receipts Tax Amounts	$ 6.8	$ 5.7