Summary of Significant Accounting Policies (Policies)	9 Months Ended
Sep. 30, 2017
Accounting Policies [Abstract]
Consolidation	The consolidated financial statements include the accounts of Anadarko and subsidiaries in which Anadarko holds, directly or indirectly, more than 50% of the voting rights and VIEs for which Anadarko is the primary beneficiary. The Company has determined that WGP and WES are VIEs. Anadarko is considered the primary beneficiary and consolidates WGP and WES. WGP and WES function with capital structures that are separate from Anadarko, consisting of their own debt instruments and publicly traded common units. All intercompany transactions have been eliminated. Undivided interests in oil and natural-gas exploration and production joint ventures are consolidated on a proportionate basis. Investments in noncontrolled entities that Anadarko has the ability to exercise significant influence over operating and financial policies and VIEs for which Anadarko is not the primary beneficiary are accounted for using the equity method. In applying the equity method of accounting, the investments are initially recognized at cost and subsequently adjusted for the Company’s proportionate share of earnings, losses, and distributions. Other investments are carried at original cost. Investments accounted for using the equity method and cost method are included in other assets.
Recently Issued Accounting Standards	Recently Adopted Accounting Standards ASU 2017-01, Business Combinations (Topic 805): Clarifying the Definition of a Business, assists in determining whether a transaction should be accounted for as an acquisition or disposal of assets or as a business. This ASU provides a screen that when substantially all of the fair value of the gross assets acquired, or disposed of, are concentrated in a single identifiable asset, or a group of similar identifiable assets, the assets will not be considered a business. If the screen is not met, the assets must include an input and a substantive process that together significantly contribute to the ability to create an output to be considered a business. The Company’s adoption of this ASU on January 1, 2017, using a prospective approach, could have a material impact on consolidated financial statements as goodwill will not be allocated to divestitures or recorded on acquisitions that are not considered businesses. See Note 3—Acquisitions, Divestitures, and Assets Held for Sale. ASU 2016-16, Income Taxes (Topic 740): Intra-Entity Transfers of Assets Other Than Inventory, requires an entity to recognize the income tax consequences of an intra-entity transfer of an asset other than inventory when the transfer occurs and eliminates the exception for an intra-entity transfer of an asset other than inventory. The Company adopted this ASU on January 1, 2017, using a modified retrospective approach, and recognized a cumulative adjustment to retained earnings of $31 million during the first quarter of 2017. 1. Summary of Significant Accounting Policies (Continued) ASU 2016-09, Compensation—Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting, simplifies the accounting for share-based payment transactions, including the income tax consequences, classification on the statement of cash flows, accounting for forfeitures, and classification of awards as either equity or liabilities. As a result of adopting this ASU on January 1, 2017, excess tax benefits and tax deficiencies related to share-based compensation are reflected on a prospective basis in the income statement as a component of the provision for income taxes rather than additional paid-in capital as previously recognized. For the nine months ended September 30, 2017, the Company recognized a $13 million tax deficiency as an increase to the provision for income taxes. Cash flows related to excess tax benefits are classified on a prospective basis as operating activities in the statement of cash flows rather than cash inflows from financing activities and cash outflows from operating activities as previously recognized. Prior periods of the statement of cash flows were not adjusted as there was no material impact. In addition, the Company elected to begin accounting for share-based compensation award forfeitures when they occur instead of estimating the number of forfeitures expected. This change in accounting policy for share-based compensation award forfeitures did not have a material impact on the Company’s consolidated financial statements. New Accounting Standards Issued But Not Yet Adopted ASU 2017-07, Compensation—Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost, requires presentation of service cost in the same line item(s) as other compensation costs arising from services rendered by employees during the period and presentation of the remaining components of net benefit cost in a separate line item outside operating items. Additionally, only the service cost component of net benefit cost will be eligible for capitalization. The Company will adopt this ASU on January 1, 2018, with retrospective presentation of the service cost component and the other components of net benefit cost in the income statement and prospective presentation for the capitalization of the service cost component of net benefit cost in assets. Upon adoption, non-service cost components of net periodic benefit costs of $225 million for the year ended 2016 and $94 million for the nine months ended September 30, 2017, will be reclassified to other (income) expense, net, from G&A; oil and gas operating; gathering, processing, and marketing; and exploration expense. The Company does not expect any other material changes upon adoption of this ASU. ASU 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash, requires an entity to explain the changes in the total of cash, cash equivalents, restricted cash, and restricted cash equivalents on the statement of cash flows and to provide a reconciliation of the totals in that statement to the related captions in the balance sheet when the cash, cash equivalents, restricted cash, and restricted cash equivalents are presented in more than one line item on the balance sheet. This ASU is effective for annual and interim periods beginning after December 15, 2017, and is required to be adopted using a retrospective approach, with early adoption permitted. The Company will adopt this ASU on January 1, 2018, and does not expect the adoption to have a material impact on its consolidated financial statements. ASU 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments, provides clarification on how certain cash receipts and cash payments are presented and classified on the statement of cash flows. This ASU is effective for annual and interim periods beginning after December 15, 2017, and is required to be adopted using a retrospective approach if practicable, with early adoption permitted. The Company will adopt this ASU on January 1, 2018, and does not expect the adoption to have a material impact on its Consolidated Statement of Cash Flows. 1. Summary of Significant Accounting Policies (Continued) ASU 2014-09, Revenue from Contracts with Customers (Topic 606), supersedes current revenue recognition requirements and requires an entity to recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration the entity expects to be entitled to in exchange for those goods or services. Additional disclosures will be required to describe the nature, amount, timing, and uncertainty of revenue and cash flows from contracts with customers. The Company has completed an initial review of contracts in each of its revenue streams and is developing accounting policies to address the provisions of the ASU. While the Company does not currently expect net earnings to be materially impacted, the Company has concluded that it is acting as an agent in the sale of certain volumes on behalf of its midstream service customers based on the requirements of the new ASU. This conclusion will result in the reduction of gathering and processing revenues and a corresponding reduction to gathering and processing expense related to its contracts with these customers. In addition, the Company expects to recognize revenue for commodities received as noncash consideration in exchange for services provided by our midstream business and revenue and associated cost of product for the subsequent sale of those same commodities. This recognition will result in an increase to revenues and expenses for gathering and processing activities with no impact on net earnings. The Company also expects changes in the timing of recognizing revenue for certain fees earned from its midstream business and hard minerals royalties due to the fee structure of certain contracts. Anadarko continues to evaluate the impact of these and other provisions of the ASU on its accounting policies, internal controls, and consolidated financial statements. Although the Company has not finalized the quantitative impact of the new standard, based on the assessment completed to date, the Company does not expect the adoption of this standard will have a material impact on its net earnings. The Company will complete its evaluation during the fourth quarter of 2017 and will adopt this new standard on January 1, 2018, using the modified retrospective method with a cumulative adjustment to retained earnings. ASU 2016-02, Leases (Topic 842), requires lessees to recognize a lease liability and a right-of-use asset for all leases, including operating leases, with a term greater than 12 months on the balance sheet. The provisions of ASU 2016-02 also modify the definition of a lease and outline the requirements for recognition, measurement, presentation, and disclosure of leasing arrangements by both lessees and lessors. Anadarko plans to elect certain practical expedients when implementing the new lease standard, which means the Company will not have to reassess the accounting for contracts that commenced prior to adoption. Anadarko has preliminarily determined its portfolio of leased assets and is reviewing all related contracts to determine the impact that adoption will have on its consolidated financial statements. The Company is also evaluating the impact of this ASU on its systems, processes, and internal controls. The Company will complete its evaluation in 2018 and adopt this new standard on January 1, 2019, using a modified retrospective approach for all comparative periods presented.

Recently Adopted Accounting Standards ASU 2017-01, Business Combinations (Topic 805): Clarifying the Definition of a Business, assists in determining whether a transaction should be accounted for as an acquisition or disposal of assets or as a business. This ASU provides a screen that when substantially all of the fair value of the gross assets acquired, or disposed of, are concentrated in a single identifiable asset, or a group of similar identifiable assets, the assets will not be considered a business. If the screen is not met, the assets must include an input and a substantive process that together significantly contribute to the ability to create an output to be considered a business. The Company’s adoption of this ASU on January 1, 2017, using a prospective approach, could have a material impact on consolidated financial statements as goodwill will not be allocated to divestitures or recorded on acquisitions that are not considered businesses. See Note 3—Acquisitions, Divestitures, and Assets Held for Sale.

ASU 2016-16, Income Taxes (Topic 740): Intra-Entity Transfers of Assets Other Than Inventory, requires an entity to recognize the income tax consequences of an intra-entity transfer of an asset other than inventory when the transfer occurs and eliminates the exception for an intra-entity transfer of an asset other than inventory. The Company adopted this ASU on January 1, 2017, using a modified retrospective approach, and recognized a cumulative adjustment to retained earnings of $31 million during the first quarter of 2017.

1. Summary of Significant Accounting Policies (Continued)

ASU 2016-09, Compensation—Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting, simplifies the accounting for share-based payment transactions, including the income tax consequences, classification on the statement of cash flows, accounting for forfeitures, and classification of awards as either equity or liabilities. As a result of adopting this ASU on January 1, 2017, excess tax benefits and tax deficiencies related to share-based compensation are reflected on a prospective basis in the income statement as a component of the provision for income taxes rather than additional paid-in capital as previously recognized. For the nine months ended September 30, 2017, the Company recognized a $13 million tax deficiency as an increase to the provision for income taxes. Cash flows related to excess tax benefits are classified on a prospective basis as operating activities in the statement of cash flows rather than cash inflows from financing activities and cash outflows from operating activities as previously recognized. Prior periods of the statement of cash flows were not adjusted as there was no material impact. In addition, the Company elected to begin accounting for share-based compensation award forfeitures when they occur instead of estimating the number of forfeitures expected. This change in accounting policy for share-based compensation award forfeitures did not have a material impact on the Company’s consolidated financial statements.

New Accounting Standards Issued But Not Yet Adopted ASU 2017-07, Compensation—Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost, requires presentation of service cost in the same line item(s) as other compensation costs arising from services rendered by employees during the period and presentation of the remaining components of net benefit cost in a separate line item outside operating items. Additionally, only the service cost component of net benefit cost will be eligible for capitalization. The Company will adopt this ASU on January 1, 2018, with retrospective presentation of the service cost component and the other components of net benefit cost in the income statement and prospective presentation for the capitalization of the service cost component of net benefit cost in assets. Upon adoption, non-service cost components of net periodic benefit costs of $225 million for the year ended 2016 and $94 million for the nine months ended September 30, 2017, will be reclassified to other (income) expense, net, from G&A; oil and gas operating; gathering, processing, and marketing; and exploration expense. The Company does not expect any other material changes upon adoption of this ASU.

ASU 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash, requires an entity to explain the changes in the total of cash, cash equivalents, restricted cash, and restricted cash equivalents on the statement of cash flows and to provide a reconciliation of the totals in that statement to the related captions in the balance sheet when the cash, cash equivalents, restricted cash, and restricted cash equivalents are presented in more than one line item on the balance sheet. This ASU is effective for annual and interim periods beginning after December 15, 2017, and is required to be adopted using a retrospective approach, with early adoption permitted. The Company will adopt this ASU on January 1, 2018, and does not expect the adoption to have a material impact on its consolidated financial statements.

ASU 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments, provides clarification on how certain cash receipts and cash payments are presented and classified on the statement of cash flows. This ASU is effective for annual and interim periods beginning after December 15, 2017, and is required to be adopted using a retrospective approach if practicable, with early adoption permitted. The Company will adopt this ASU on January 1, 2018, and does not expect the adoption to have a material impact on its Consolidated Statement of Cash Flows.

1. Summary of Significant Accounting Policies (Continued)

ASU 2014-09, Revenue from Contracts with Customers (Topic 606), supersedes current revenue recognition requirements and requires an entity to recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration the entity expects to be entitled to in exchange for those goods or services. Additional disclosures will be required to describe the nature, amount, timing, and uncertainty of revenue and cash flows from contracts with customers. The Company has completed an initial review of contracts in each of its revenue streams and is developing accounting policies to address the provisions of the ASU. While the Company does not currently expect net earnings to be materially impacted, the Company has concluded that it is acting as an agent in the sale of certain volumes on behalf of its midstream service customers based on the requirements of the new ASU. This conclusion will result in the reduction of gathering and processing revenues and a corresponding reduction to gathering and processing expense related to its contracts with these customers. In addition, the Company expects to recognize revenue for commodities received as noncash consideration in exchange for services provided by our midstream business and revenue and associated cost of product for the subsequent sale of those same commodities. This recognition will result in an increase to revenues and expenses for gathering and processing activities with no impact on net earnings. The Company also expects changes in the timing of recognizing revenue for certain fees earned from its midstream business and hard minerals royalties due to the fee structure of certain contracts. Anadarko continues to evaluate the impact of these and other provisions of the ASU on its accounting policies, internal controls, and consolidated financial statements. Although the Company has not finalized the quantitative impact of the new standard, based on the assessment completed to date, the Company does not expect the adoption of this standard will have a material impact on its net earnings. The Company will complete its evaluation during the fourth quarter of 2017 and will adopt this new standard on January 1, 2018, using the modified retrospective method with a cumulative adjustment to retained earnings.

ASU 2016-02, Leases (Topic 842), requires lessees to recognize a lease liability and a right-of-use asset for all leases, including operating leases, with a term greater than 12 months on the balance sheet. The provisions of ASU 2016-02 also modify the definition of a lease and outline the requirements for recognition, measurement, presentation, and disclosure of leasing arrangements by both lessees and lessors. Anadarko plans to elect certain practical expedients when implementing the new lease standard, which means the Company will not have to reassess the accounting for contracts that commenced prior to adoption. Anadarko has preliminarily determined its portfolio of leased assets and is reviewing all related contracts to determine the impact that adoption will have on its consolidated financial statements. The Company is also evaluating the impact of this ASU on its systems, processes, and internal controls. The Company will complete its evaluation in 2018 and adopt this new standard on January 1, 2019, using a modified retrospective approach for all comparative periods presented.