Debt and Financing Arrangements (Notes)	6 Months Ended
Jun. 30, 2018
Debt Disclosure [Abstract]
Debt and Financing Arrangements	DEBT AND FINANCING ARRANGEMENTS Credit Facility We along with WPZ and Northwest Pipeline LLC (Northwest Pipeline), are party to a credit facility with aggregate commitments available of $3.5 billion, with up to an additional $500 million increase in aggregate commitments available under certain circumstances. Total letter of credit capacity available to WPZ under this credit facility is $1.125 billion. We are able to borrow up to $500 million under this credit facility to the extent not otherwise utilized by the other co-borrowers. At June 30, 2018, no letters of credit have been issued and no loans were outstanding under the credit facility. WPZ participates in a commercial paper program, and WPZ management considers amounts outstanding under this program to be a reduction of available capacity under the credit facility. The program allows a maximum outstanding amount at any time of $3 billion of unsecured commercial paper notes. At June 30, 2018, WPZ had no commercial paper outstanding under the commercial paper program. During July 2018, in anticipation of the WPZ Merger closing, Williams entered into a new $4.5 billion unsecured revolving credit agreement (Credit Agreement) that includes us and Northwest Pipeline as co-borrowers. The full amount of the credit facility will be available to Williams to the extent not utilized by us and Northwest Pipeline. Both Transco and Northwest Pipeline will have access up to $500 million under this Credit Agreement. The Credit Agreement will become effective upon closing of the WPZ Merger and will be initially available for five years from the Credit Agreement effective date. Other Financing Obligation During the first six months of 2018, we received an additional $24.3 million of funding from a co-owner for its proportionate share of construction costs related to its undivided ownership interest in the Dalton lateral. This additional funding is reflected in Long-Term Debt on our Condensed Consolidated Balance Sheet. At June 30, 2018, the amount included in Long-Term Debt on our Condensed Consolidated Balance Sheet for this financing obligation is $252.8 million, and the amount included in Long-term debt due within one year on our Condensed Consolidated Balance Sheet for this financing obligation is $1.6 million. Issuance and Retirement of Long-Term Debt On March 15, 2018, we issued $400 million of 4.0 percent senior unsecured notes due 2028 and $600 million of 4.6 percent senior unsecured notes due 2048 to investors in a private placement. We used the net proceeds to retire our $250 million of 6.05 percent senior unsecured notes due June 2018, and for general purposes, including the funding of capital expenditures. As part of the issuance, we entered into a registration rights agreement with the initial purchasers of the unsecured notes. We are obligated to file and consummate a registration statement for an offer to exchange the notes for a new issue of substantially identical notes registered under the Securities Act of 1933, as amended, within 365 days from closing and to use commercially reasonable efforts to complete the exchange offer. We are required to provide a shelf registration statement to cover resales of the notes under certain circumstances. If we fail to fulfill these obligations, additional interest will accrue on the affected securities. The rate of additional interest will be 0.25 percent per annum on the principal amount of the affected securities for the first 90-day period immediately following the occurrence of a registration default, increasing by an additional 0.25 percent per annum with respect to each subsequent 90-day period thereafter, up to a maximum amount for all such registration defaults of 0.5 percent annually. Following the cure of any registration defaults, the accrual of additional interest will cease.

DEBT AND FINANCING ARRANGEMENTS

Credit Facility

We along with WPZ and Northwest Pipeline LLC (Northwest Pipeline), are party to a credit facility with aggregate commitments available of $3.5 billion, with up to an additional $500 million increase in aggregate commitments available under certain circumstances. Total letter of credit capacity available to WPZ under this credit facility is $1.125 billion. We are able to borrow up to $500 million under this credit facility to the extent not otherwise utilized by the other co-borrowers. At June 30, 2018, no letters of credit have been issued and no loans were outstanding under the credit facility.

WPZ participates in a commercial paper program, and WPZ management considers amounts outstanding under this program to be a reduction of available capacity under the credit facility. The program allows a maximum outstanding amount at any time of $3 billion of unsecured commercial paper notes. At June 30, 2018, WPZ had no commercial paper outstanding under the commercial paper program.

During July 2018, in anticipation of the WPZ Merger closing, Williams entered into a new $4.5 billion unsecured revolving credit agreement (Credit Agreement) that includes us and Northwest Pipeline as co-borrowers. The full amount of the credit facility will be available to Williams to the extent not utilized by us and Northwest Pipeline. Both Transco and Northwest Pipeline will have access up to $500 million under this Credit Agreement. The Credit Agreement will become effective upon closing of the WPZ Merger and will be initially available for five years from the Credit Agreement effective date.

Other Financing Obligation

During the first six months of 2018, we received an additional $24.3 million of funding from a co-owner for its proportionate share of construction costs related to its undivided ownership interest in the Dalton lateral. This additional funding is reflected in Long-Term Debt on our Condensed Consolidated Balance Sheet. At June 30, 2018, the amount included in Long-Term Debt on our Condensed Consolidated Balance Sheet for this financing obligation is $252.8 million, and the amount included in Long-term debt due within one year on our Condensed Consolidated Balance Sheet for this financing obligation is $1.6 million.

Issuance and Retirement of Long-Term Debt

On March 15, 2018, we issued $400 million of 4.0 percent senior unsecured notes due 2028 and $600 million of 4.6 percent senior unsecured notes due 2048 to investors in a private placement. We used the net proceeds to retire our $250 million of 6.05 percent senior unsecured notes due June 2018, and for general purposes, including the funding of capital expenditures. As part of the issuance, we entered into a registration rights agreement with the initial purchasers of the unsecured notes. We are obligated to file and consummate a registration statement for an offer to exchange the notes for a new issue of substantially identical notes registered under the Securities Act of 1933, as amended, within 365 days from closing and to use commercially reasonable efforts to complete the exchange offer. We are required to provide a shelf registration statement to cover resales of the notes under certain circumstances. If we fail to fulfill these obligations, additional interest will accrue on the affected securities. The rate of additional interest will be 0.25 percent per annum on the principal amount of the affected securities for the first 90-day period immediately following the occurrence of a registration default, increasing by an additional 0.25 percent per annum with respect to each subsequent 90-day period thereafter, up to a maximum amount for all such registration defaults of 0.5 percent annually. Following the cure of any registration defaults, the accrual of additional interest will cease.