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Note 6 - Long-term Debt - Composition of Long-term Debt (Details) - USD ($) $ in Millions | Sep. 30, 2022 | Sep. 30, 2021
--- | --- | ---
Total principal of long-term debt | $ 3,258.9 | $ 3,014.6
Less: Unamortized discounts and debt issuance costs | (19.2) | (19.7)
Less: Current portion | (281.2) | (55.8)
Long-term debt (less current portion) | 2,958.5 | 2,939.1
Spire Missouri [Member] |  |
Total principal of long-term debt | 1,648.0 | 1,348.0
Less: Unamortized discounts and debt issuance costs | (10.3) | (9.6)
Less: Current portion | (250.0) | 0.0
Long-term debt (less current portion) | 1,387.7 | 1,338.4
Spire Alabama Inc [Member] |  |
Total principal of long-term debt | 575.0 | 625.0
Less: Unamortized discounts and debt issuance costs | (3.5) | (3.8)
Less: Current portion | 0.0 | (50.0)
Long-term debt (less current portion) | 571.5 | 571.2
First Mortgage Bonds Three Percentage Series Due March152023 [Member] | Spire Missouri [Member] |  |
Total principal of long-term debt | 250.0 | 250.0
Floating Rate Series Due December 2, 2024 [Member] | Spire Missouri [Member] |  |
Total principal of long-term debt | 300.0 |
First Mortgage Bonds Three Point Four Percentage Series Due August152023 [Member] | Spire Missouri [Member] |  |
Total principal of long-term debt | 45.0 | 45.0
First Mortgage Bonds Three Point Four Percentage Series Due March152028 [Member] | Spire Missouri [Member] |  |
Total principal of long-term debt | 19.3 | 19.3
First Mortgage Bonds Seven Percentage Series Due June12029 [Member] | Spire Missouri [Member] |  |
Total principal of long-term debt | 275.0 | 275.0
First Mortgage Bonds Two Point Eight Four Percentage Series Due November152029 [Member] | Spire Missouri [Member] |  |
Total principal of long-term debt | 30.0 | 30.0
First Mortgage Bonds Seven Point Nine Percentage Series Due September152030 [Member] | Spire Missouri [Member] |  |
Total principal of long-term debt | 50.0 | 50.0
First Mortgage Bonds Three Point Six Eight Percentage Series Due September152032 [Member] | Spire Missouri [Member] |  |
Total principal of long-term debt | 99.3 | 99.3
First Mortgage Bonds Six Percentage Series Due May12034 [Member] | Spire Missouri [Member] |  |
Total principal of long-term debt | 54.5 | 54.5
First Mortgage Bonds Six Point One Five Percentage Series Due June12036 [Member] | Spire Missouri [Member] |  |
Total principal of long-term debt | 99.9 | 99.9
First Mortgage Bonds Four Point Six Three Percentage Series Due August152043 [Member] | Spire Missouri [Member] |  |
Total principal of long-term debt | 70.0 | 70.0
First Mortgage Bonds Four Point Two Three Percentage Series Due September152047 [Member] | Spire Missouri [Member] |  |
Total principal of long-term debt | 305.0 | 305.0
First Mortgage Bonds Three Point Three Zero Percentage Series Due June12051 [Member] | Spire Missouri [Member] |  |
Total principal of long-term debt | 50.0 | 50.0
Three Point Eight Six Percentage Notes Due December222021 [Member] | Spire Alabama Inc [Member] |  |
Total principal of long-term debt | 0.0 | 50.0
Three Point Two One Percentage Notes Due September152025 [Member] | Spire Alabama Inc [Member] |  |
Total principal of long-term debt | 35.0 | 35.0
Two Point Eight Eight Percentage Notes Due December12029 [Member] | Spire Alabama Inc [Member] |  |
Total principal of long-term debt | 100.0 | 100.0
Two Point Zero Four Percentage Notes Due December152030 [Member] | Spire Alabama Inc [Member] |  |
Total principal of long-term debt | 150.0 | 150.0
Five Point Nine Zero Percentage Notes Due January152037 [Member] | Spire Alabama Inc [Member] |  |
Total principal of long-term debt | 45.0 | 45.0
Four Point Three One Percentage Notes Due December12045 [Member] | Spire Alabama Inc [Member] |  |
Total principal of long-term debt | 80.0 | 80.0
Three Point Nine Two Percentage Notes Due January152048 [Member] | Spire Alabama Inc [Member] |  |
Total principal of long-term debt | 45.0 | 45.0
Four Point Six Four Percentage Notes Due January152049 [Member] | Spire Alabama Inc [Member] |  |
Total principal of long-term debt | 90.0 | 90.0
Four Point Zero Two Percentage Notes Due January152058 [Member] | Spire Alabama Inc [Member] |  |
Total principal of long-term debt | 30.0 | 30.0
Parent Company [Member] | Three Point Three One Percent Notes Payable Due December152022 [Member] |  |
Total principal of long-term debt | 25.0 | 25.0
Parent Company [Member] | Three Point Five Four Percent Senior Notes Due February272024 [Member] |  |
Total principal of long-term debt | 150.0 | 150.0
Parent Company [Member] | Zero Point Seven Five Percent Remarketable Senior Notes Due March12026 [Member] |  |
Total principal of long-term debt | 175.0 | 175.0
Parent Company [Member] | Two Point Five Two Percent Senior Notes Due September 1 2021 [Member] |  |
Total principal of long-term debt | 130.0 | 130.0
Parent Company [Member] | Three Point One Three Percent Senior Notes Due September12026 [Member] |  |
Total principal of long-term debt | 100.0 | 100.0
Parent Company [Member] | Three Point Nine Three Percent Senior Notes Due March152027 [Member] |  |
Total principal of long-term debt | 250.0 | 250.0
Subsidiaries [Member] |  |
Total principal of long-term debt | 205.9 |
Subsidiaries [Member] | Four Point One Four Percent First Mortgage Bonds Due September302021 [Member] |  |
Total principal of long-term debt | 42.0 | 42.0
Subsidiaries [Member] | Two Nine Five Percent Notes With Annual Principal Payments Through December2034 [Member] |  |
Total principal of long-term debt | 123.9 | 129.6
Subsidiaries [Member] | Five Percent First Mortgage Bonds Due September302031 [Member] |  |
Total principal of long-term debt | $ 40.0 | $ 40.0

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