Impact of the Tax Cuts and Jobs Act of 2017	3 Months Ended
Dec. 31, 2018
Income Tax Disclosure [Abstract]
Impact of the Tax Cuts and Jobs Act of 2017	Impact of the Tax Cuts and Jobs Act of 2017 On December 22, 2017, the Tax Cuts and Jobs Act of 2017 (the "TCJA") was signed into law. As a result of the implementation of the TCJA, we recognized a $161.9 million income tax benefit in our condensed consolidated statement of comprehensive income during the first quarter of fiscal 2018 related to a change in deferred taxes that were not related to our cost of service ratemaking. The change in deferred taxes related to our cost of service ratemaking (referred to as excess deferred taxes) was reclassified into a regulatory liability and will be returned to ratepayers in accordance with regulatory requirements. As of December 31, 2018 and September 30, 2018, this liability totaled $740.9 million and $744.9 million. We have and continue to work with our regulators in each jurisdiction to fully incorporate the effects of the TCJA into customer bills. As of December 31, 2018, we have received approval from regulators to update our cost of service rates to reflect the decrease in the statutory income tax rate in our Colorado, Kansas, Kentucky, Louisiana, Mississippi, Tennessee and Texas service areas. We continue to work with regulators in Virginia to reflect the effects of the lower statutory income tax rate in our cost of service in rates. Regulators in all of our service areas issued accounting orders that required us to establish, effective January 1, 2018, a separate regulatory liability for the difference in taxes included in our rates that were calculated based on a 35% statutory income tax rate and rates based on the new 21% statutory income tax rate until the new rates could be established. As of December 31, 2018, we received approval from regulators to return these liabilities to customers in Colorado, Kansas, Louisiana and Texas. This regulatory liability totaled $19.3 million and $22.5 million as of December 31, 2018 and September 30, 2018. As of December 31, 2018, we received approval from regulators to return excess deferred taxes in Colorado, Kentucky, Louisiana, Mississippi, Tennessee and Texas in accordance with regulatory proceedings on a provisional basis over periods ranging from 13 to 51 years. In our remaining jurisdictions, the treatment of the effects of the TCJA in rates is being addressed in ongoing or will be addressed in future regulatory proceedings. The SEC issued guidance in Staff Accounting Bulletin 118 (SAB 118), which allowed us to record provisional amounts during a one-year measurement period, similar to the measurement period in accounting for business combinations. The Company recorded provisional amounts for the income tax effects of the TCJA for the fiscal year ended September 30, 2018. Although the Company no longer considers the accounting effects of the TCJA to be provisional under SAB 118, many aspects of the TCJA remain unclear and its impact on the Company's income tax balances may change following further interpretation of TCJA provisions by issuance of U.S. Treasury regulations or guidance from the Internal Revenue Service. We continue to monitor and assess the accounting implications of the TCJA developments on the consolidated financial statements.

Impact of the Tax Cuts and Jobs Act of 2017

On December 22, 2017, the Tax Cuts and Jobs Act of 2017 (the "TCJA") was signed into law. As a result of the implementation of the TCJA, we recognized a $161.9 million income tax benefit in our condensed consolidated statement of comprehensive income during the first quarter of fiscal 2018 related to a change in deferred taxes that were not related to our cost of service ratemaking. The change in deferred taxes related to our cost of service ratemaking (referred to as excess deferred taxes) was reclassified into a regulatory liability and will be returned to ratepayers in accordance with regulatory requirements. As of December 31, 2018 and September 30, 2018, this liability totaled $740.9 million and $744.9 million.

We have and continue to work with our regulators in each jurisdiction to fully incorporate the effects of the TCJA into customer bills. As of December 31, 2018, we have received approval from regulators to update our cost of service rates to reflect the decrease in the statutory income tax rate in our Colorado, Kansas, Kentucky, Louisiana, Mississippi, Tennessee and Texas service areas. We continue to work with regulators in Virginia to reflect the effects of the lower statutory income tax rate in our cost of service in rates.

Regulators in all of our service areas issued accounting orders that required us to establish, effective January 1, 2018, a separate regulatory liability for the difference in taxes included in our rates that were calculated based on a 35% statutory income tax rate and rates based on the new 21% statutory income tax rate until the new rates could be established. As of December 31, 2018, we received approval from regulators to return these liabilities to customers in Colorado, Kansas, Louisiana and Texas. This regulatory liability totaled $19.3 million and $22.5 million as of December 31, 2018 and September 30, 2018.

As of December 31, 2018, we received approval from regulators to return excess deferred taxes in Colorado, Kentucky, Louisiana, Mississippi, Tennessee and Texas in accordance with regulatory proceedings on a provisional basis over periods ranging from 13 to 51 years. In our remaining jurisdictions, the treatment of the effects of the TCJA in rates is being addressed in ongoing or will be addressed in future regulatory proceedings.

The SEC issued guidance in Staff Accounting Bulletin 118 (SAB 118), which allowed us to record provisional amounts during a one-year measurement period, similar to the measurement period in accounting for business combinations. The Company recorded provisional amounts for the income tax effects of the TCJA for the fiscal year ended September 30, 2018. Although the Company no longer considers the accounting effects of the TCJA to be provisional under SAB 118, many aspects of the TCJA remain unclear and its impact on the Company's income tax balances may change following further interpretation of TCJA provisions by issuance of U.S. Treasury regulations or guidance from the Internal Revenue Service. We continue to monitor and assess the accounting implications of the TCJA developments on the consolidated financial statements.