Income Taxes	9 Months Ended
Income Taxes	Jun. 30, 2020
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The effective tax rates for the quarters ended June 30, 2020 and June 30, 2019 were 24.1% and 24.9%, respectively. The decrease in the tax rate for the quarter is mainly due to an increase in the allowance for funds used during construction (which is not taxable) as a result of certain ongoing projects in our Pipeline and Storage segment. The effective tax rates for the nine months ended June 30, 2020 and June 30, 2019 were 78.9% and 22.3%, respectively. The increase in the tax rate is primarily the result of the valuation allowance recorded against certain state deferred tax assets, discussed below, as well as the elimination of the Enhanced Oil Recovery tax credit in fiscal 2020. A valuation allowance for deferred tax assets, including net operating losses and tax credits, is recognized when it is more likely than not that some or all of the benefit from the deferred tax assets will not be realized. Consistent with the prior quarter, as of June 30, 2020, the Company recorded a valuation allowance against certain state deferred tax assets in the amount of $57.7 million based on its conclusion, considering all available evidence (both positive and negative), that it was more likely than not that the deferred tax assets would not be realized. Changes in judgment regarding future realization of these deferred tax assets may result in a reversal of all or a portion of the valuation allowance. The Company will continue to re-assess this position each quarter. Prior to the “Coronavirus Aid, Relief and Economic Security (CARES) Act" (discussed below), the 2017 Tax Reform Act repealed the corporate alternative minimum tax (AMT) and provided that the Company’s existing AMT credit carryovers were refundable, if not utilized to reduce tax, beginning in fiscal 2019. As of September 30, 2018, the Company had $85.0 million of AMT credit carryovers that were expected to be refunded between fiscal 2020 and fiscal 2023, if not previously utilized. The Company received the first installment for $42.5 million of AMT credit refunds related to fiscal 2019 in January 2020. On March 27, 2020, the CARES Act was signed into law. The CARES Act, among other things, includes provisions relating to AMT credit refunds, refundable payroll tax credits, deferment of employer side social security payments, net operating loss carryback periods, and modifications to the net interest deduction limitation. The Company filed for the acceleration of the remaining AMT credit refunds (under CARES) of $42.5 million, which were received in June 2020.

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.