Unaudited Financial Information (Policies)	3 Months Ended
Unaudited Financial Information (Policies)	Dec. 31, 2020
Accounting Policies [Abstract]
Accounting pronouncements adopted and not yet adopted	Accounting pronouncements adopted in fiscal 2021 Effective October 1, 2020, we adopted new accounting guidance that requires credit losses on most financial assets measured at amortized cost and certain other instruments to be measured using an expected credit loss model. Under this model, we estimate credit losses over the entire contractual term of the instrument from the date of initial recognition of that instrument. The new guidance also introduces a new impairment recognition model for available-for-sale debt securities that will require credit losses to be recorded through an allowance account. We adopted the new guidance using a modified retrospective method. The adoption of this standard did not have a material impact on our financial position, results of operations and cash flows and no adjustments were made to October 1, 2020 opening balances as a result of this adoption. As required under the modified retrospective method of adoption, results for the reporting period beginning after October 1, 2020 are presented under Accounting Standards Codification (ASC) 326, while prior period amounts are not adjusted. See Notes 5 and 11 to the unaudited condensed consolidated financial statements for further discussion of implementation of the standard. Accounting pronouncements that will be effective after fiscal 2021 In March 2020, the Financial Accounting Standards Board (FASB) issued optional guidance which will ease the potential burden in accounting for or recognizing the effects of reference rate reform on financial reporting. The amendments provide optional expedients and exceptions for applying U.S. GAAP to contracts, hedging relationships and other transactions affected by the cessation of the London Interbank Offered Rate (LIBOR). The amendments can be elected immediately, as of March 12, 2020, through December 31, 2022. We are currently evaluating if we will apply the optional guidance as we assess the impact of the cessation of LIBOR on our current contracts and hedging relationships and the potential impact on our financial position, results of operations and cash flows.
Regulatory assets and liabilities	Regulatory assets and liabilities Accounting principles generally accepted in the United States require cost-based, rate-regulated entities that meet certain criteria to reflect the authorized recovery of costs due to regulatory decisions in their financial statements. As a result, certain costs are permitted to be capitalized rather than expensed because they can be recovered through rates. We record certain costs as regulatory assets when future recovery through customer rates is considered probable. Regulatory liabilities are recorded when it is probable that revenues will be reduced for amounts that will be credited to customers through the ratemaking process. Substantially all of our regulatory assets are recorded as a component of deferred charges and other assets and our regulatory liabilities are recorded as a component of other current liabilities and deferred credits and other liabilities. Deferred gas costs are recorded either in other current assets or liabilities and our regulatory excess deferred taxes and regulatory cost of removal obligation are reported separately.
Earnings per share	We use the two-class method of computing earnings per share because we have participating securities in the form of non-vested restricted stock units with a nonforfeitable right to dividend equivalents, for which vesting is predicated solely on the passage of time. The calculation of earnings per share using the two-class method excludes income attributable to these participating securities from the numerator and excludes the dilutive impact of those shares from the denominator. Basic weighted average shares outstanding is calculated based upon the weighted average number of common shares outstanding during the periods presented. Also, this calculation includes fully vested stock awards that have not yet been issued as common stock. Additionally, the weighted average shares outstanding for diluted EPS includes the incremental effects of the forward sale agreements, discussed in Note 7 to the unaudited condensed consolidated financial statements, when the impact is dilutive.
Fair value measurement	Fair Value MeasurementsWe report certain assets and liabilities at fair value, which is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date (exit price). We record cash and cash equivalents, accounts receivable and accounts payable at carrying value, which substantially approximates fair value due to the short-term nature of these assets and liabilities. For other financial assets and liabilities, we primarily use quoted market prices and other observable market pricing information to minimize the use of unobservable pricing inputs in our measurements when determining fair value. The methods used to determine fair value for our assets and liabilities are fully described in Note 2 to the consolidated financial statements in our Annual Report on Form 10-K for the fiscal year ended September 30, 2020. During the three months ended December 31, 2020, there were no changes in these methods.