XML 44 R31.htm IDEA: XBRL DOCUMENT
v3.21.1

Summary of Significant Accounting Policies - Accrued Capital Expenditures (Details) - USD ($) $ in Millions | 6 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2021 | Mar. 31, 2020 | Sep. 30, 2020
Schedule Of Accrued Capital Expenditures Excluded From Statement Of Cash Flow [Line Items] |  |  |
Accruals for capital expenditures | $ 36.1 | $ 51.4 | $ 67.6
Spire Missouri |  |  |
Schedule Of Accrued Capital Expenditures Excluded From Statement Of Cash Flow [Line Items] |  |  |
Accruals for capital expenditures | 21.8 | 21.5 | 34.3
Spire Alabama |  |  |
Schedule Of Accrued Capital Expenditures Excluded From Statement Of Cash Flow [Line Items] |  |  |
Accruals for capital expenditures | $ 4.7 | $ 17.6 | $ 17.0

X
- Definition [Line Items] for Schedule of Accrued Capital Expenditures Excluded from Statement of Cash Flow [Table] + References No definition available. + Details
Name: | sr_ScheduleOfAccruedCapitalExpendituresExcludedFromStatementOfCashFlowLineItems
Namespace Prefix: | sr_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Future cash outflow to pay for purchases of fixed assets that have occurred. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=121583591&loc=d3e4332-108586 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=121583591&loc=d3e4313-108586 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=121583591&loc=d3e4304-108586 + Details
Name: | us-gaap_CapitalExpendituresIncurredButNotYetPaid
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Details
Name: | dei_LegalEntityAxis=sr_SpireMissouriMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | dei_LegalEntityAxis=sr_SpireAlabamaIncMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |