Regulatory Matters	9 Months Ended
Regulatory Matters	Sep. 30, 2016
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Matters	Regulatory Matters Columbia Gas Transmission Modernization Program. In November 2015, Columbia Gas Transmission commenced the fourth year of the Columbia Gas Transmission long-term system modernization program. Columbia Gas Transmission expects to place approximately $300.0 million in modernization investments into service during the year. Recovery of the revenue requirement on approximately $320.0 million of investments made in 2015 began on February 1, 2016. In December 2015, Columbia Gas Transmission filed an extension of this settlement and received the FERC's approval of the customer agreement in March 2016. This extension will allow Columbia Gas Transmission to invest an additional $1.1 billion over an additional three-year period through 2020. This agreement also expands the scope of facility investments covered by the program. Columbia Gulf. On January 21, 2016, the FERC issued an Order (the "January 21 Order") initiating an investigation pursuant to Section 5 of the NGA to determine whether Columbia Gulf’s existing rates for jurisdictional services are unjust and unreasonable. Columbia Gulf filed a cost and revenue study with the FERC on April 5, 2016, as required by the January 21 Order. The January 21 Order directed that a hearing be conducted pursuant to an accelerated timeline and that an initial decision be issued by February 28, 2017. On June 13, 2016, the FERC trial staff, Columbia Gulf, and all of the active parties filed a Joint Motion to Suspend the Procedural Schedule and Waive Answer Period (the "Motion"). The Motion represents that the parties unanimously support the Motion and requested waiver of the answer period, which was granted. The parties reached an agreement in principle during a June 2, 2016 settlement conference that would fully resolve all matters set for hearing by the FERC. The Motion represents that the parties expect to file an offer of settlement memorializing the agreement in principle no later than July 29, 2016, and suspension of the procedural schedule will promote an efficient and speedy resolution of this matter by allowing the participants to focus their efforts on drafting the necessary settlement documents. Columbia Gulf filed the offer of settlement with the FERC in accordance with the agreement noted above. On August 15, 2016, the administrative law judge issued a Certification of Uncontested Settlement, which noted that no parties objected to the provisions in the offer of settlement. On September 22, 2016, the FERC issued an order approving the uncontested settlement, which requires a reduction in Columbia Gulf’s daily maximum recourse rate and addresses Columbia Gulf’s treatment of postretirement benefits other than pensions, pension expenses, and regulatory expenses. The order also requires Columbia Gulf to file a general rate case under section 4 of the NGA by January 31, 2020, for rates to take effect by August 1, 2020. Other terms of the settlement are included in FERC Docket No. RP16-302-000. Cost Recovery Trackers and other similar mechanisms. A significant portion of the transmission and storage regulated companies' revenue is related to the recovery of their operating costs, the review and recovery of which occurs via standard regulatory proceedings with the FERC under Section 4 of the NGA. However, certain operating costs of the Columbia OpCo regulated transmission and storage companies are significant and recurring in nature, such as fuel for compression and lost and unaccounted for gas. The FERC allows for the recovery of such costs via cost tracking mechanisms. These tracking mechanisms allow the transmission and storage companies' rates to fluctuate in response to changes in certain operating costs or conditions as they occur to facilitate the timely recovery of its costs incurred. The tracking mechanisms involve a rate adjustment that is filed at a predetermined frequency, typically annually, with the FERC and is subject to regulatory review before new rates go into effect. Other such costs under regulatory tracking mechanisms include upstream pipeline transmission, electric compression, operational purchases and sales of natural gas, and the revenue requirement for capital investments made under Columbia Gas Transmission's long-term plan to modernize its interstate transmission system as discussed above.

CPG OpCo LP 10-Q