Summary of Significant Accounting Policies (Policies)	6 Months Ended
Summary of Significant Accounting Policies (Policies)	Jun. 30, 2018
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The condensed consolidated financial statements include our accounts and the accounts of our consolidated subsidiaries, including certain special purpose entities (SPEs) utilized in secured financing transactions, which are considered variable interest entities (VIEs). All intercompany transactions and accounts have been eliminated in consolidation. On October 31, 2017, we completed the sale of certain of our European subsidiaries and branches (collectively, our European Operations) to Banque PSA Finance S.A. and BNP Paribas Personal Finance S.A. The European Operations are presented as discontinued operations in our condensed consolidated financial statements for the three and six months ended June 30, 2017. Refer to Note 12 for additional details regarding our disposal of these operations. Unless otherwise indicated, information in these notes to the condensed consolidated financial statements relates to our continuing operations. The condensed consolidated financial statements, including the notes thereto, are condensed and do not include all disclosures required by generally accepted accounting principles (GAAP) in the United States of America. These condensed consolidated financial statements should be read in conjunction with the audited consolidated financial statements that are included in our Annual Report on Form 10-K filed on February 6, 2018 (Form 10-K). Except as otherwise specified, dollar amounts presented within tables are stated in millions. The condensed consolidated financial statements at June 30, 2018, and for the three and six months ended June 30, 2018 and 2017, are unaudited and, in management’s opinion, include all adjustments, which consist of normal recurring adjustments and transactions or events discretely impacting the interim periods, considered necessary by management to fairly state our results of operations. The results for interim periods are not necessarily indicative of results for a full year. The condensed consolidated balance sheet at December 31, 2017, was derived from audited annual financial statements.
Segment Information	Segment Information We are the wholly-owned captive finance subsidiary of General Motors Company (GM). We offer substantially similar products and services throughout many different regions, subject to local regulations and market conditions. We evaluate our business in two operating segments: North America (the North America Segment) and International (the International Segment). Our North America Segment includes operations in the U.S. and Canada. Our International Segment includes operations in Brazil, Chile, Colombia, Mexico and Peru, as well as our equity investment in SAIC-GMAC Automotive Finance Company Limited (SAIC-GMAC), a joint venture that conducts automobile finance operations in China.
Recently Adopted Accounting Standards	Recently Adopted Accounting Standards Effective January 1, 2018, we adopted ASU 2014-09, “Revenue from Contracts with Customers” (ASU 2014-09) as amended, as incorporated into Accounting Standards Codification (ASC) 606, on a modified retrospective basis by recognizing a cumulative effect adjustment of $33 million as an increase to the opening balance of retained earnings. Under the new standard, commission revenue and expenses related to certain retail finance receivables that were previously recognized as earned or incurred ratably over the term of the related receivables will now be recognized in full at the origination of the receivables. Effective January 1, 2018, we adopted ASU 2018-02, "Income Statement-Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income" (ASU 2018-02). ASU 2018-02 provides the option to reclassify stranded tax effects related to the U.S. Tax Cuts and Jobs Act of 2017 in accumulated other comprehensive income to retained earnings. The cumulative effect of the adjustments to the opening balance of retained earnings for the adopted standard was insignificant. Effective January 1, 2018, we adopted ASU 2017-12, "Derivatives and Hedging (Topic 815), Targeted Improvements to Accounting for Hedging Activities" (ASU 2017-12), on a modified retrospective basis, which is intended to facilitate financial reporting that more closely reflects risk management activities and simplifies the application of hedge accounting. Changes to the new guidance include expanded disclosures regarding the types of risk management strategies eligible for hedge accounting, simplifying the documentation and effectiveness assessment requirements, changing how ineffectiveness is measured, and changing the presentation and disclosure requirements for hedge accounting activities. The cumulative effect of the adjustments to the opening balance of retained earnings for the adopted standard was insignificant. The following change to our derivative accounting policy became effective upon adoption of ASU 2017-12: Certain interest rate swap and foreign currency swap agreements have been designated as cash flow hedges. The risk being hedged is the foreign currency and interest rate risk related to forecasted transactions. If the contract has been designated as a cash flow hedge, the change in the fair value of the cash flow hedge is deferred in accumulated other comprehensive loss and is recognized in interest, operating and other expenses along with the earnings effect of the hedged item when the hedged item affects earnings. Changes in the fair value of amounts excluded from the assessment of effectiveness are recorded currently in earnings and are presented in the same income statement line as the earnings effect of the hedged item.