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FINANCING ARRANGEMENTS AND LONG-TERM DEBT (Details) | Dec. 21, 2016 USD ($) | Dec. 14, 2016 USD ($) bank | Jan. 12, 2018 USD ($) | Dec. 31, 2017 USD ($) | Dec. 01, 2017 USD ($) | Sep. 30, 2017 USD ($) | Dec. 31, 2016 USD ($)
--- | --- | --- | --- | --- | --- | --- | ---
Line of Credit Facility [Line Items] |  |  |  |  |  |  |
Debt covenant, short-term debt to capital requirement, maximum |  | 70.00% |  |  |  |  |
Notes outstanding |  |  |  | $ 583,600,000 |  | $ 477,300,000 | $ 0
Commercial Paper Notes |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |
Face amount | $ 975,000,000.0 |  |  |  |  |  |
Debt term | 365 days |  |  |  |  |  |
Spire Missouri |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |
Notes outstanding |  |  |  | 275,600,000 |  |  |
Spire Alabama |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |
Notes outstanding |  |  |  | $ 163,100,000 |  |  |
Line of Credit | Revolving Credit Facility |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |
Number of banks in loan agreement | bank |  | 11 |  |  |  |  |
Maximum borrowing capacity |  | $ 975,000,000.0 |  |  |  |  |
Line of Credit | Revolving Credit Facility | Spire Missouri |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |
Maximum borrowing capacity |  | 475,000,000.0 |  |  |  |  |
Ratio of short-term debt to total capital |  |  |  | 0.50 |  |  |
Line of Credit | Revolving Credit Facility | Spire Alabama |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |
Maximum borrowing capacity |  | 200,000,000.0 |  |  |  |  |
Ratio of short-term debt to total capital |  |  |  | 0.35 |  |  |
Line of Credit | Revolving Credit Facility | Spire |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |
Maximum borrowing capacity |  | $ 300,000,000.0 |  |  |  |  |
Ratio of short-term debt to total capital |  |  |  | 0.57 |  |  |
Credit facility borrowings |  |  |  | $ 0 |  | $ 0 | $ 193,500,000
Senior Notes | Spire Alabama | Series 2017A senior notes due 2058 |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |
Face amount |  |  |  |  | $ 30,000,000 |  |
Stated interest rate |  |  |  |  | 4.02% |  |
Senior Notes | Spire Alabama | Series 2017B senior notes due 2048 | Subsequent Event |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |
Face amount |  |  | $ 45,000,000 |  |  |  |
Stated interest rate |  |  | 3.92% |  |  |  |

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- Definition The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(16)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(16)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 + Details
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