FAIR VALUE MEASUREMENTS (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Millions | Dec. 31, 2017 | Sep. 30, 2017 | Dec. 31, 2016 |
LIABILITIES | | | |
Effects of Netting and Cash Margin Receivables /Payables | $ (14) | | |
Derivative liability | 5.8 | | |
Spire Missouri | | | |
ASSETS | | | |
Effects of Netting and Cash Margin Receivables /Payables | (0.5) | $ (3.4) | $ (6.6) |
Derivative asset | 23.5 | 22.5 | 23.9 |
LIABILITIES | | | |
Effects of Netting and Cash Margin Receivables /Payables | (2.7) | (1.9) | (0.2) |
Derivative liability | 0 | 0 | 0 |
Quoted Prices in Active Markets (Level 1) | | | |
LIABILITIES | | | |
Derivative liability before netting adjustment | 3.8 | | |
Quoted Prices in Active Markets (Level 1) | Spire Missouri | | | |
ASSETS | | | |
Derivative asset before netting adjustment | 20 | 21.8 | 26.5 |
LIABILITIES | | | |
Derivative liability before netting adjustment | 2.7 | 1.9 | 0.2 |
Significant Observable Inputs (Level 2) | | | |
LIABILITIES | | | |
Derivative liability before netting adjustment | 15.6 | | |
Significant Observable Inputs (Level 2) | Spire Missouri | | | |
ASSETS | | | |
Derivative asset before netting adjustment | 4 | 4.1 | 4 |
LIABILITIES | | | |
Derivative liability before netting adjustment | 0 | 0 | 0 |
Significant Unobservable Inputs (Level 3) | | | |
LIABILITIES | | | |
Derivative liability before netting adjustment | 0.4 | | |
Significant Unobservable Inputs (Level 3) | Spire Missouri | | | |
ASSETS | | | |
Derivative asset before netting adjustment | 0 | 0 | 0 |
LIABILITIES | | | |
Derivative liability before netting adjustment | 0 | 0 | 0 |
US stock/bond mutual funds | Spire Missouri | | | |
ASSETS | | | |
Effects of Netting and Cash Margin Receivables /Payables | 0 | 0 | 0 |
Derivative asset | 23.5 | 22.4 | 21.2 |
US stock/bond mutual funds | Quoted Prices in Active Markets (Level 1) | Spire Missouri | | | |
ASSETS | | | |
Derivative asset before netting adjustment | 19.5 | 18.3 | 17.2 |
US stock/bond mutual funds | Significant Observable Inputs (Level 2) | Spire Missouri | | | |
ASSETS | | | |
Derivative asset before netting adjustment | 4 | 4.1 | 4 |
US stock/bond mutual funds | Significant Unobservable Inputs (Level 3) | Spire Missouri | | | |
ASSETS | | | |
Derivative asset before netting adjustment | 0 | 0 | 0 |
NYMEX/ICE natural gas contracts | | | |
LIABILITIES | | | |
Effects of Netting and Cash Margin Receivables /Payables | | | (0.2) |
Derivative liability | | | 0 |
NYMEX/ICE natural gas contracts | Spire Missouri | | | |
ASSETS | | | |
Effects of Netting and Cash Margin Receivables /Payables | (0.5) | (3.4) | (6.6) |
Derivative asset | 0 | 0 | 2.2 |
LIABILITIES | | | |
Effects of Netting and Cash Margin Receivables /Payables | (2.7) | (1.9) | |
Derivative liability | 0 | 0 | |
NYMEX/ICE natural gas contracts | Quoted Prices in Active Markets (Level 1) | | | |
LIABILITIES | | | |
Derivative liability before netting adjustment | | | 0.2 |
NYMEX/ICE natural gas contracts | Quoted Prices in Active Markets (Level 1) | Spire Missouri | | | |
ASSETS | | | |
Derivative asset before netting adjustment | 0.5 | 3.4 | 8.8 |
LIABILITIES | | | |
Derivative liability before netting adjustment | 2.7 | 1.9 | |
NYMEX/ICE natural gas contracts | Significant Observable Inputs (Level 2) | | | |
LIABILITIES | | | |
Derivative liability before netting adjustment | | | 0 |
NYMEX/ICE natural gas contracts | Significant Observable Inputs (Level 2) | Spire Missouri | | | |
ASSETS | | | |
Derivative asset before netting adjustment | 0 | 0 | 0 |
LIABILITIES | | | |
Derivative liability before netting adjustment | 0 | 0 | |
NYMEX/ICE natural gas contracts | Significant Unobservable Inputs (Level 3) | | | |
LIABILITIES | | | |
Derivative liability before netting adjustment | | | 0 |
NYMEX/ICE natural gas contracts | Significant Unobservable Inputs (Level 3) | Spire Missouri | | | |
ASSETS | | | |
Derivative asset before netting adjustment | 0 | 0 | 0 |
LIABILITIES | | | |
Derivative liability before netting adjustment | 0 | 0 | |
Gasoline and heating oil contracts | Spire Missouri | | | |
ASSETS | | | |
Effects of Netting and Cash Margin Receivables /Payables | | 0 | 0 |
Derivative asset | | 0.1 | 0.5 |
Gasoline and heating oil contracts | Quoted Prices in Active Markets (Level 1) | Spire Missouri | | | |
ASSETS | | | |
Derivative asset before netting adjustment | | 0.1 | 0.5 |
Gasoline and heating oil contracts | Significant Observable Inputs (Level 2) | Spire Missouri | | | |
ASSETS | | | |
Derivative asset before netting adjustment | | 0 | 0 |
Gasoline and heating oil contracts | Significant Unobservable Inputs (Level 3) | Spire Missouri | | | |
ASSETS | | | |
Derivative asset before netting adjustment | | 0 | 0 |
Other | Interest rate swaps | | | |
LIABILITIES | | | |
Effects of Netting and Cash Margin Receivables /Payables | 0 | 0 | |
Derivative liability | 0.8 | 0.9 | |
Other | Interest rate swaps | Quoted Prices in Active Markets (Level 1) | | | |
LIABILITIES | | | |
Derivative liability before netting adjustment | 0 | 0 | |
Other | Interest rate swaps | Significant Observable Inputs (Level 2) | | | |
LIABILITIES | | | |
Derivative liability before netting adjustment | 0.8 | 0.9 | |
Other | Interest rate swaps | Significant Unobservable Inputs (Level 3) | | | |
LIABILITIES | | | |
Derivative liability before netting adjustment | 0 | 0 | |
Gas Utility | US stock/bond mutual funds | | | |
ASSETS | | | |
Effects of Netting and Cash Margin Receivables /Payables | 0 | 0 | 0 |
Derivative asset | 23.5 | 22.4 | 21.2 |
Gas Utility | US stock/bond mutual funds | Quoted Prices in Active Markets (Level 1) | | | |
ASSETS | | | |
Derivative asset before netting adjustment | 19.5 | 18.3 | 17.2 |
Gas Utility | US stock/bond mutual funds | Significant Observable Inputs (Level 2) | | | |
ASSETS | | | |
Derivative asset before netting adjustment | 4 | 4.1 | 4 |
Gas Utility | US stock/bond mutual funds | Significant Unobservable Inputs (Level 3) | | | |
ASSETS | | | |
Derivative asset before netting adjustment | 0 | 0 | 0 |
Gas Utility | NYMEX/ICE natural gas contracts | | | |
ASSETS | | | |
Effects of Netting and Cash Margin Receivables /Payables | (0.5) | (3.4) | (6.6) |
Derivative asset | 0 | 0 | 2.2 |
LIABILITIES | | | |
Effects of Netting and Cash Margin Receivables /Payables | (2.7) | (1.9) | (0.2) |
Derivative liability | 0 | 0 | 0 |
Gas Utility | NYMEX/ICE natural gas contracts | Quoted Prices in Active Markets (Level 1) | | | |
ASSETS | | | |
Derivative asset before netting adjustment | 0.5 | 3.4 | 8.8 |
LIABILITIES | | | |
Derivative liability before netting adjustment | 2.7 | 1.9 | 0.2 |
Gas Utility | NYMEX/ICE natural gas contracts | Significant Observable Inputs (Level 2) | | | |
ASSETS | | | |
Derivative asset before netting adjustment | 0 | 0 | 0 |
LIABILITIES | | | |
Derivative liability before netting adjustment | 0 | 0 | 0 |
Gas Utility | NYMEX/ICE natural gas contracts | Significant Unobservable Inputs (Level 3) | | | |
ASSETS | | | |
Derivative asset before netting adjustment | 0 | 0 | 0 |
LIABILITIES | | | |
Derivative liability before netting adjustment | 0 | 0 | 0 |
Gas Utility | Gasoline and heating oil contracts | | | |
ASSETS | | | |
Effects of Netting and Cash Margin Receivables /Payables | | 0 | 0 |
Derivative asset | | 0.1 | 0.7 |
Gas Utility | Gasoline and heating oil contracts | Quoted Prices in Active Markets (Level 1) | | | |
ASSETS | | | |
Derivative asset before netting adjustment | | 0.1 | 0.7 |
Gas Utility | Gasoline and heating oil contracts | Significant Observable Inputs (Level 2) | | | |
ASSETS | | | |
Derivative asset before netting adjustment | | 0 | 0 |
Gas Utility | Gasoline and heating oil contracts | Significant Unobservable Inputs (Level 3) | | | |
ASSETS | | | |
Derivative asset before netting adjustment | | 0 | 0 |
Gas Marketing | | | |
ASSETS | | | |
Effects of Netting and Cash Margin Receivables /Payables | (10.9) | (6.7) | |
Derivative asset | 27.2 | 28.7 | |
LIABILITIES | | | |
Effects of Netting and Cash Margin Receivables /Payables | | (5.2) | (10.4) |
Derivative liability | | 8.1 | 3.5 |
Gas Marketing | Quoted Prices in Active Markets (Level 1) | | | |
ASSETS | | | |
Derivative asset before netting adjustment | 22.4 | 23.1 | |
LIABILITIES | | | |
Derivative liability before netting adjustment | | 3.7 | 5.3 |
Gas Marketing | Significant Observable Inputs (Level 2) | | | |
ASSETS | | | |
Derivative asset before netting adjustment | 15.7 | 12.2 | |
LIABILITIES | | | |
Derivative liability before netting adjustment | | 9.6 | 8.6 |
Gas Marketing | Significant Unobservable Inputs (Level 3) | | | |
ASSETS | | | |
Derivative asset before netting adjustment | 0 | 0.1 | |
LIABILITIES | | | |
Derivative liability before netting adjustment | | 0 | 0 |
Gas Marketing | US stock/bond mutual funds | | | |
ASSETS | | | |
Effects of Netting and Cash Margin Receivables /Payables | | | (11.8) |
Derivative asset | | | 42.1 |
Gas Marketing | US stock/bond mutual funds | Quoted Prices in Active Markets (Level 1) | | | |
ASSETS | | | |
Derivative asset before netting adjustment | | | 27.4 |
Gas Marketing | US stock/bond mutual funds | Significant Observable Inputs (Level 2) | | | |
ASSETS | | | |
Derivative asset before netting adjustment | | | 26.5 |
Gas Marketing | US stock/bond mutual funds | Significant Unobservable Inputs (Level 3) | | | |
ASSETS | | | |
Derivative asset before netting adjustment | | | 0 |
Gas Marketing | NYMEX/ICE natural gas contracts | | | |
ASSETS | | | |
Effects of Netting and Cash Margin Receivables /Payables | (6.1) | (2.1) | (4.9) |
Derivative asset | 0.3 | 0.5 | 0.3 |
LIABILITIES | | | |
Effects of Netting and Cash Margin Receivables /Payables | (7) | (2.1) | (9.9) |
Derivative liability | 0 | 0 | 0 |
Gas Marketing | NYMEX/ICE natural gas contracts | Quoted Prices in Active Markets (Level 1) | | | |
ASSETS | | | |
Derivative asset before netting adjustment | 2.4 | 1.3 | 0.7 |
LIABILITIES | | | |
Derivative liability before netting adjustment | 1.1 | 1.8 | 5.1 |
Gas Marketing | NYMEX/ICE natural gas contracts | Significant Observable Inputs (Level 2) | | | |
ASSETS | | | |
Derivative asset before netting adjustment | 4 | 1.3 | 4.5 |
LIABILITIES | | | |
Derivative liability before netting adjustment | 5.9 | 0.3 | 4.8 |
Gas Marketing | NYMEX/ICE natural gas contracts | Significant Unobservable Inputs (Level 3) | | | |
ASSETS | | | |
Derivative asset before netting adjustment | 0 | 0 | 0 |
LIABILITIES | | | |
Derivative liability before netting adjustment | 0 | 0 | 0 |
Gas Marketing | Natural gas commodity contracts | | | |
ASSETS | | | |
Effects of Netting and Cash Margin Receivables /Payables | (4.3) | (1.2) | (0.3) |
Derivative asset | 3.4 | 5.7 | 9.5 |
LIABILITIES | | | |
Effects of Netting and Cash Margin Receivables /Payables | (4.3) | (1.2) | (0.3) |
Derivative liability | 5 | 7.2 | 3.5 |
Gas Marketing | Natural gas commodity contracts | Quoted Prices in Active Markets (Level 1) | | | |
ASSETS | | | |
Derivative asset before netting adjustment | 0 | 0 | 0 |
LIABILITIES | | | |
Derivative liability before netting adjustment | 0 | 0 | 0 |
Gas Marketing | Natural gas commodity contracts | Significant Observable Inputs (Level 2) | | | |
ASSETS | | | |
Derivative asset before netting adjustment | 7.7 | 6.8 | 9.8 |
LIABILITIES | | | |
Derivative liability before netting adjustment | 8.9 | 8.4 | 3.8 |
Gas Marketing | Natural gas commodity contracts | Significant Unobservable Inputs (Level 3) | | | |
ASSETS | | | |
Derivative asset before netting adjustment | 0 | 0.1 | 0 |
LIABILITIES | | | |
Derivative liability before netting adjustment | $ 0.4 | $ 0 | 0 |
Gas Marketing | Other | | | |
ASSETS | | | |
Effects of Netting and Cash Margin Receivables /Payables | | | 0 |
Derivative asset | | | 8.2 |
Gas Marketing | Other | Quoted Prices in Active Markets (Level 1) | | | |
ASSETS | | | |
Derivative asset before netting adjustment | | | 0 |
Gas Marketing | Other | Significant Observable Inputs (Level 2) | | | |
ASSETS | | | |
Derivative asset before netting adjustment | | | 8.2 |
Gas Marketing | Other | Significant Unobservable Inputs (Level 3) | | | |
ASSETS | | | |
Derivative asset before netting adjustment | | | $ 0 |