Rate and Regulatory Matters (Notes)	12 Months Ended
Dec. 31, 2017
Public Utilities, Rate Matters [Abstract]
Public Utilities, Disclosure of Rate Matters [Text Block]	RATE AND REGULATORY MATTERS Rates Our rates became effective January 1, 2018, and are expected to remain in effect for 5 years. 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 2017 Settlement, 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. As a result of Tax Reform, a regulatory liability of $23.6 million will be recorded annually for the period beginning January 1, 2018, and continuing through the time that our current rates remain effective. This liability will be amortized back to our customers over a five-year period, coincidental with the next rate case going into effect. Further, as a result of the decreased federal income tax rates, deferrals for timing differences related to accelerated tax deductions recorded on our books were reflected at the previous statutory tax rates and will need to be reduced to the new statutory tax rates. The timing and actual amount of such return will be subject to future negotiations regarding this matter and many other elements of cost-of-service rate proceedings, including the other costs of providing services. We recorded a regulatory liability for this difference.

RATE AND REGULATORY MATTERS

Rates

Our rates became effective January 1, 2018, and are expected to remain in effect for 5 years.

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 2017 Settlement, 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. As a result of Tax Reform, a regulatory liability of $23.6 million will be recorded annually for the period beginning January 1, 2018, and continuing through the time that our current rates remain effective. This liability will be amortized back to our customers over a five-year period, coincidental with the next rate case going into effect.

Further, as a result of the decreased federal income tax rates, deferrals for timing differences related to accelerated tax deductions recorded on our books were reflected at the previous statutory tax rates and will need to be reduced to the new statutory tax rates. The timing and actual amount of such return will be subject to future negotiations regarding this matter and many

other elements of cost-of-service rate proceedings, including the other costs of providing services. We recorded a regulatory liability for this difference.