Debt and Financing Arrangements (Notes)	9 Months Ended
Sep. 30, 2018
Debt Disclosure [Abstract]
Debt and Financing Arrangements	DEBT AND FINANCING ARRANGEMENTS Credit Facility Effective August 2018, we along with Williams and Northwest Pipeline LLC (Northwest Pipeline), entered into and are party to a credit facility with aggregate commitments available of $4.5 billion, with up to an additional $500 million increase in aggregate commitments available under certain circumstances. Total letter of credit capacity available to Williams under this credit facility is $1 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 September 30, 2018, no letters of credit have been issued and no loans were outstanding under the credit facility. On August 10, 2018, following the consummation of the WPZ Merger, WPZ's $3 billion commercial paper program was discontinued and Williams entered into a new $4 billion commercial paper program. Williams management considers amounts outstanding under this program to be a reduction of available capacity under the credit facility. At September 30, 2018, Williams had approximately $824 million of commercial paper outstanding. Other Financing Obligation During the first nine months of 2018, we received an additional $29.2 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 September 30, 2018, the amount included in Long-Term Debt on our Condensed Consolidated Balance Sheet for this financing obligation is $257.3 million, and the amount included in Long-term debt due within one year on our Condensed Consolidated Balance Sheet for this financing obligation is $1.7 million. During the construction of our Atlantic-Sunrise project, we received funding from a partner for its proportionate share of construction costs related to an undivided ownership interest in certain parts of the project. Amounts received were recorded in Advances for construction costs and 100 percent of the costs associated with construction were capitalized on our Condensed Consolidated Balance Sheet. Upon placing the project in service during October 2018, we began utilizing this partner's undivided interest in the lateral, including the associated pipeline capacity, and expect to reclassify approximately $789.8 million, as of the balance sheet date, of funding previously received from our partner from Advances for construction costs to debt to reflect the financing obligation payable to our partner over an expected term of 20 years. As this transaction did not meet the criteria for sale leaseback accounting due to our continued involvement, it will be accounted for as a financing arrangement over the course of the capacity agreement. 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. In September 2018, we completed an exchange of these notes for substantially identical new notes that are registered under the Securities Act of 1933, as amended.

DEBT AND FINANCING ARRANGEMENTS

Credit Facility

Effective August 2018, we along with Williams and Northwest Pipeline LLC (Northwest Pipeline), entered into and are party to a credit facility with aggregate commitments available of $4.5 billion, with up to an additional $500 million increase in aggregate commitments available under certain circumstances. Total letter of credit capacity available to Williams under this credit facility is $1 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 September 30, 2018, no letters of credit have been issued and no loans were outstanding under the credit facility.

On August 10, 2018, following the consummation of the WPZ Merger, WPZ's $3 billion commercial paper program was discontinued and Williams entered into a new $4 billion commercial paper program. Williams management considers amounts outstanding under this program to be a reduction of available capacity under the credit facility. At September 30, 2018, Williams had approximately $824 million of commercial paper outstanding.

Other Financing Obligation

During the first nine months of 2018, we received an additional $29.2 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 September 30, 2018, the amount included in Long-Term Debt on our Condensed Consolidated Balance Sheet for this financing obligation is $257.3 million, and the amount included in Long-term debt due within one year on our Condensed Consolidated Balance Sheet for this financing obligation is $1.7 million.

During the construction of our Atlantic-Sunrise project, we received funding from a partner for its proportionate share of construction costs related to an undivided ownership interest in certain parts of the project. Amounts received were recorded in Advances for construction costs and 100 percent of the costs associated with construction were capitalized on our Condensed Consolidated Balance Sheet. Upon placing the project in service during October 2018, we began utilizing this partner's undivided interest in the lateral, including the associated pipeline capacity, and expect to reclassify approximately $789.8 million, as of the balance sheet date, of funding previously received from our partner from Advances for construction costs to debt to reflect the financing obligation payable to our partner over an expected term of 20 years. As this transaction did not meet the criteria for sale leaseback accounting due to our continued involvement, it will be accounted for as a financing arrangement over the course of the capacity agreement.

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. In September 2018, we completed an exchange of these notes for substantially identical new notes that are registered under the Securities Act of 1933, as amended.