Rate and Regulatory Matters (Notes)	6 Months Ended
Jun. 30, 2018
Public Utilities, Rate Matters [Abstract]
Public Utilities, Disclosure of Rate Matters [Text Block]	RATE AND REGULATORY MATTERS Rate Case Settlement Filing On January 23, 2017, we filed for FERC approval a Stipulation and Settlement Agreement (Settlement) and were assigned Docket No. RP17-346. The Settlement specified an annual cost of service of $440 million and established a new general system firm Rate Schedule TF-1 (Large Customer) demand rate of $0.39294/Dth with a $0.00832 commodity rate (Phase 1) and a demand rate of $0.39033/Dth with a $0.00832 commodity rate (Phase 2). Phase 1 rates became effective January 1, 2018, with the Phase 2 rates becoming effective October 1, 2018. The annual cost of service does not change from Phase 1 to Phase 2, but the Phase 2 rates reflect the termination of fifteen-year levelized contracts that will now become Rate Schedule TF-1 (Large Customer) contracts. Provisions were included in the Settlement that we can file a general rate case to place new rates into effect after October 1, 2018, and that a general rate case must be filed for new rates to become effective no later than January 1, 2023. Tax Reform Rates charged to our customers are subject to the rate-making policies of the FERC. These policies permit an interstate pipeline to include in its cost-of-service an income tax allowance that includes a deferred income tax component. The recently enacted Tax Cuts and Jobs Act signed into law on December 22, 2017 (Tax Reform), among other things, reduces the corporate federal income tax rates. As part of our Settlement discussed above, we agreed with our customers to record a regulatory asset or liability for federal income tax rate increases or decreases due to subsequent legislation, such as Tax Reform. Therefore, we have established a regulatory liability of $11.8 million as of June 30, 2018, included within Regulatory Liabilities in our Balance Sheet. This liability will be amortized over a five-year period, coincidental with the next rate case going into effect. Recent FERC Developments On March 15, 2018, the FERC issued a revised policy statement in Docket No. PL17-1 regarding the recovery of income tax costs in rates of natural gas pipelines. The FERC found that an impermissible double recovery results from granting a Master Limited Partnership (MLP) pipeline both an income tax allowance and a return on equity pursuant to the discounted cash flow methodology. As a result, the FERC will no longer permit a MLP pipeline to recover an income tax allowance in its cost of service. The FERC further stated it will address the application of this policy to non-MLP partnership forms as those issues arise in subsequent proceedings. On July 18, 2018, the FERC issued an order dismissing the requests for rehearing and clarification of the revised policy statement. In addition, the FERC provided guidance that an MLP pipeline (or other pass-through entity) no longer recovering an income tax allowance pursuant to the revised policy may eliminate previously accumulated deferred income taxes (ADIT) from its cost of service instead of flowing these previously accumulated ADIT balances to ratepayers. However, the FERC stated that the revised policy statement and such guidance do not establish a binding rule, but are instead expressions of general policy intent designed to provide guidance by notifying entities of the course of action the FERC intends to follow in future adjudications. To the extent the FERC addresses these issues in future proceedings, it will consider any arguments regarding not only the application of the revised policy to the facts of the case, but also any arguments regarding the underlying validity of the policy itself. On March 15, 2018, the FERC also issued a Notice of Proposed Rulemaking in Docket No. RM18-11 proposing a filing process that will allow it to determine which natural gas pipelines may be collecting unjust and unreasonable rates in light of the recent reduction in the corporate income tax rate in Tax Reform and the revised policy statement. On July 18, 2018, the FERC issued a Final Rule in the docket, retaining the filing requirement and reaffirming the options that pipelines have to either reflect the reduced tax rate or explain why no rate change is necessary. The FERC also clarified that a natural gas company organized as a pass-through entity all of whose income or losses are consolidated on the federal income tax return of its corporate parent is considered to be subject to the federal corporate income tax, and is thus eligible for a tax allowance. On March 15, 2018, the FERC also issued a Notice of Inquiry in Docket No. RM18-12 seeking comments on the additional impacts of Tax Reform on jurisdictional rates, particularly whether, and if so how, the FERC should address changes relating to accumulated deferred income tax amounts after the corporate income tax rate reduction and bonus depreciation rules, as well as whether other features of Tax Reform require FERC action. We are evaluating the impact of these developments and currently expect any associated impacts would be prospective and determined through subsequent rate proceedings. We also continue to monitor developments that may impact our regulatory liabilities resulting from Tax Reform. It is reasonably possible that our future tariff-based rates collected may be adversely impacted.

RATE AND REGULATORY MATTERS

Rate Case Settlement Filing

On January 23, 2017, we filed for FERC approval a Stipulation and Settlement Agreement (Settlement) and were assigned Docket No. RP17-346. The Settlement specified an annual cost of service of $440 million and established a new general system firm Rate Schedule TF-1 (Large Customer) demand rate of $0.39294/Dth with a $0.00832 commodity rate (Phase 1) and a demand rate of $0.39033/Dth with a $0.00832 commodity rate (Phase 2). Phase 1 rates became effective January 1, 2018, with the Phase 2 rates becoming effective October 1, 2018. The annual cost of service does not change from Phase 1 to Phase 2, but the Phase 2 rates reflect the termination of fifteen-year levelized contracts that will now become Rate Schedule TF-1 (Large Customer) contracts. Provisions were included in the Settlement that we can file a general rate case to place new rates into effect after October 1, 2018, and that a general rate case must be filed for new rates to become effective no later than January 1, 2023.

Tax Reform

Rates charged to our customers are subject to the rate-making policies of the FERC. These policies permit an interstate pipeline to include in its cost-of-service an income tax allowance that includes a deferred income tax component. The recently enacted Tax Cuts and Jobs Act signed into law on December 22, 2017 (Tax Reform), among other things, reduces the corporate federal income tax rates. As part of our Settlement discussed above, we agreed with our customers to record a regulatory asset or liability for federal income tax rate increases or decreases due to subsequent legislation, such as Tax Reform. Therefore, we have established a regulatory liability of $11.8 million as of June 30, 2018, included within Regulatory Liabilities in our Balance Sheet. This liability will be amortized over a five-year period, coincidental with the next rate case going into effect.

Recent FERC Developments

On March 15, 2018, the FERC issued a revised policy statement in Docket No. PL17-1 regarding the recovery of income tax costs in rates of natural gas pipelines. The FERC found that an impermissible double recovery results from granting a Master Limited Partnership (MLP) pipeline both an income tax allowance and a return on equity pursuant to the discounted cash flow methodology. As a result, the FERC will no longer permit a MLP pipeline to recover an income tax allowance in its cost of service. The FERC further stated it will address the application of this policy to non-MLP partnership forms as those issues arise in subsequent proceedings.

On July 18, 2018, the FERC issued an order dismissing the requests for rehearing and clarification of the revised policy statement. In addition, the FERC provided guidance that an MLP pipeline (or other pass-through entity) no longer recovering an income tax allowance pursuant to the revised policy may eliminate previously accumulated deferred income taxes (ADIT) from its cost of service instead of flowing these previously accumulated ADIT balances to ratepayers. However, the FERC stated that the revised policy statement and such guidance do not establish a binding rule, but are instead expressions of general policy intent designed to provide guidance by notifying entities of the course of action the FERC intends to follow in future adjudications. To the extent the FERC addresses these issues in future proceedings, it will consider any arguments regarding not only the application of the revised policy to the facts of the case, but also any arguments regarding the underlying validity of the policy itself.

On March 15, 2018, the FERC also issued a Notice of Proposed Rulemaking in Docket No. RM18-11 proposing a filing process that will allow it to determine which natural gas pipelines may be collecting unjust and unreasonable rates in light of the recent reduction in the corporate income tax rate in Tax Reform and the revised policy statement. On July 18, 2018, the FERC issued a Final Rule in the docket, retaining the filing requirement and reaffirming the options that pipelines have to either reflect the reduced tax rate or explain why no rate change is necessary. The FERC also clarified that a natural gas company organized as a pass-through entity all of whose income or losses are consolidated on the federal income tax return of its corporate parent is considered to be subject to the federal corporate income tax, and is thus eligible for a tax allowance.

On March 15, 2018, the FERC also issued a Notice of Inquiry in Docket No. RM18-12 seeking comments on the additional impacts of Tax Reform on jurisdictional rates, particularly whether, and if so how, the FERC should address changes relating to accumulated deferred income tax amounts after the corporate income tax rate reduction and bonus depreciation rules, as well as whether other features of Tax Reform require FERC action. We are evaluating the impact of these developments and currently expect any associated impacts would be prospective and determined through subsequent rate proceedings. We also continue to monitor developments that may impact our regulatory liabilities resulting from Tax Reform. It is reasonably possible that our future tariff-based rates collected may be adversely impacted.