Significant Accounting Policies (Policies)	6 Months Ended
Significant Accounting Policies (Policies)	Jun. 30, 2018
Policy (Text Block) [Abstract]
Basis of Presentation	The preparation of Consolidated Financial Statements in conformity with accounting principles generally accepted in the United States of America (GAAP) requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, revenues and expenses, and the disclosures of contingent assets and liabilities. These accounting estimates reflect the best judgment of management, but actual results could differ. Discount Revenue Discount revenue primarily represents the amount we earn on transactions occurring at merchants that have entered into a card acceptance agreement with us, or a Global Network Services (GNS) partner or other third-party merchant acquirer, for facilitating transactions between the merchants and Card Members. The amount of fees charged, or merchant discount, varies with, among other factors, the industry in which the merchant conducts business, the merchant’s overall transaction volume, the timing and method of payment to the merchant, the method of submission of transactions and, in certain instances, the geographic scope of the card acceptance agreement signed with us (e.g., local or global) and the transaction amount. The merchant discount is generally deducted from the payment to the merchant and recorded as discount revenue at the time the Card Member transaction occurs. The card acceptance agreements, which outline the agreed-upon terms for charging the merchant discount fee, vary in duration. Our contracts with small- and medium-sized merchants generally have no fixed contractual duration, while those with large merchants are generally for fixed periods, which typically range from three to seven years in duration. Our fixed-period agreements may include auto-renewal features, which may allow the existing terms to continue beyond the stated expiration date until a new agreement is reached. We satisfy our obligations under these agreements over the contract term, often on a daily basis, through the processing of Card Member transactions and the availability of our payment network. In cases where the merchant acquirer is a third party (which is the case, for example, under our OptBlue program, or with certain of our GNS partners), we receive a network rate fee in our settlement with the merchant acquirer, which is individually negotiated between us and that merchant acquirer and is recorded as discount revenue at the time the Card Member transaction occurs. In our role as the operator of the American Express network, we also settle with merchants on behalf of our GNS card issuing partners, who in turn receive an issuer rate that is individually negotiated between that issuer and us and is recorded as expense in Marketing and business development (see below) or as contra-revenue in Other revenue. In contrast with networks such as those operated by Visa Inc. and Mastercard Incorporated, there are no collectively set interchange rates or network rates on the American Express network, and no fees are agreed or due between the GNS partners on the network. Net Card Fees Net card fees represent revenue earned from annual card membership fees, which vary based on the type of card and the number of cards for each account. These fees, net of acquisition costs and a reserve for projected refunds for Card Member cancellations, are deferred and recognized on a straight-line basis over the twelve-month card membership period as Net Card Fees in the Consolidated Statements of Income. The unamortized net card fee balance is reported in Other Liabilities on the Consolidated Balance Sheets. Other Fees and Commissions Other fees and commissions includes certain fees charged to Card Members, including delinquency fees and foreign currency conversion fees, which are primarily recognized in the period in which they are charged to the Card Member. Other fees and commissions also includes Membership Rewards program fees, which are deferred and recognized over the period covered by the fee, typically one year, the unamortized portion of which is included in Other Liabilities on the Consolidated Balance Sheets. In addition, Other fees and commissions includes loyalty coalition-related fees, travel commissions and fees and service fees earned from merchants, that are recognized when the service is performed, which is generally in the period the fee is charged. Refer to Note 13 for additional information. Contra-revenue Payments made through contractual arrangements with our merchants, GNS partners, and other customers are classified as expense where we receive goods, services or other benefits, for which the fair value is determinable and measurable. If these conditions are not met, the payment is classified as contra-revenue with the related revenue transaction (e.g., Discount revenue or Other revenue) and recorded when incurred. Interest Income Interest on Card Member loans is assessed using the average daily balance method. Unless the loan is classified as non-accrual, interest is recognized based upon the principal amount outstanding, in accordance with the terms of the applicable account agreement, until the outstanding balance is paid, or written off. Interest and dividends on investment securities primarily relate to our performing fixed-income securities. Interest income is recognized as earned using the effective interest method, which adjusts the yield for security premiums and discounts, fees and other payments, so that a constant rate of return is recognized on the investment security’s outstanding balance. Amounts are recognized until securities are in default or when it becomes likely that future interest payments will not be made as scheduled. Interest on deposits with banks and other is recognized as earned, and primarily relates to the placement of cash, in excess of near-term funding requirements, in interest-bearing time deposits, overnight sweep accounts, and other interest-bearing demand and call accounts. Interest Expense Interest expense includes interest incurred primarily to fund Card Member loans and receivables, general corporate purposes and liquidity needs, and is recognized as incurred. Interest expense is divided principally into two categories: (i) deposits, which primarily relates to interest expense on deposits taken from customers and institutions, and (ii) debt, which primarily relates to interest expense on our long-term debt and short-term borrowings, as well as the realized impact of derivatives used to hedge interest rate risk on our long-term debt. Marketing and Business Development As further described below under “Recently Adopted Accounting Standards,” effective January 1, 2018, in conjunction with the adoption of the new revenue recognition standard, the previously disclosed “Marketing and Promotion” line on the Consolidated Statements of Income was changed to “Marketing and Business Development” to reflect the inclusion of certain reclassified costs from Contra-discount revenue and Other expenses. Marketing and business development provides a more comprehensive view of costs related to building and growing our business, including the reclassified costs. Marketing and business development expense includes costs incurred in the development and initial placement of advertising, which are expensed in the year in which the advertising first takes place. Also included in Marketing and business development expense are Card Member statement credits for qualifying charges on eligible card accounts, corporate incentive payments earned on achievement of preset targets, and certain payments to GNS card issuing partners. These costs are generally expensed as incurred. Card Member Rewards We issue charge and credit cards that allow Card Members to participate in various rewards programs (e.g., Membership Rewards, cobrand and cash back). Rewards expense is recognized in the period Card Members earn rewards, generally by spending on their enrolled card products. We record a Card Member rewards liability that represents the estimated cost of points earned that are expected to be redeemed. Card Member rewards liabilities are impacted over time by enrollment levels, attrition, the volume of points earned and redeemed, and the associated redemption costs. Changes in the Card Member rewards liabilities during the period are taken as a charge or release to the Card Member rewards line. Effective January 1, 2018, in conjunction with the new revenue recognition standard, Card Member rewards also includes cash-back rewards, which were reclassified from contra discount revenue. Effective January 1, 2018, we adopted new revenue recognition guidance issued by the FASB related to contracts with customers. The scope of the new guidance excludes financial instruments such as credit and charge card arrangements. We elected to adopt the standard using the full retrospective method, which we believe is most useful to our investors. Under the full retrospective method, we are applying the standard back to January 1, 2016. As shown below, the most significant impacts of adoption are changes to the classification of certain revenues and expenses, including certain credit and charge card related costs previously netted against discount revenue, such as Card Member cash-back reward costs and statement credits, corporate incentive payments, as well as payments to third-party GNS card issuing partners. Under the new revenue standard, these costs are not considered components of the transaction price of our card acceptance agreements with merchants and thus are not netted against discount revenue, but instead are recognized as expenses. Our payments to third-party GNS card issuing partners are presented net of related revenues earned from the partners. The adoption of the new guidance also resulted in changes to the recognition timing of certain revenues, the impact of which is not material to net income. Similarly, the adoption did not have a material impact on our Consolidated Balance Sheets or Statements of Cash Flows. We had no material contract assets, contract liabilities or deferred contract costs recorded on the Consolidated Balance Sheet as of June 30, 2018 and December 31, 2017. Contracts assets and liabilities are reported in a net position on a contract-by-contract basis at the end of each reporting period. In adopting the guidance, we implemented changes to our accounting policies, business processes, systems and internal controls to support the recognition, measurement and disclosure requirements under the new standard. Such changes were not material. In January 2016, the FASB issued new accounting guidance on the recognition and measurement of financial assets and financial liabilities, which was effective and adopted by us as of January 1, 2018. The guidance makes targeted changes to GAAP; specifically to the classification and measurement of equity securities, and to certain disclosure requirements associated with the fair value of financial assets and liabilities. This applies to investments we make in non-public companies in the ordinary course of business, which historically were recognized under the cost method of accounting. These investments will be prospectively adjusted through earnings for observable price changes upon the identification of identical or similar transactions of the same company. The adoption of the guidance did not have a material impact on our financial position, results of operations and cash flows. We implemented changes to our accounting policies, business processes and internal controls in support of the new guidance. Such changes were not material. In August 2017, the FASB issued new accounting guidance providing targeted improvements to the accounting for hedging activities, effective January 1, 2019, with early adoption permitted in any interim period or fiscal year before the effective date. The guidance introduces a number of amendments, several of which are optional, that are designed to simplify the application of hedge accounting, improve financial statement transparency and more closely align hedge accounting with an entity’s risk management strategies. Effective January 1, 2018, we adopted the guidance, with no material impact on our financial position, results of operations and cash flows, along with associated changes to our accounting policies, business processes and internal controls in support of the new guidance. Such changes were not material.
Investments	Investment securities principally include available-for-sale debt securities carried at fair value on the Consolidated Balance Sheets, with unrealized gains and losses recorded in AOCI, net of income taxes. Realized gains and losses are recognized upon disposition of the securities using the specific identification method. Investment securities also include equity securities carried at fair value on the Consolidated Balance Sheets Effective January 1, 2018, the unrealized gains and losses on equity securities are recorded in the Consolidated Statements of Income; prior to January 1, 2018, the unrealized gains and losses on equity securities were recorded in AOCI, net of income taxes.
Contingencies	We have accrued for certain of our outstanding legal proceedings. An accrual is recorded when it is both (a) probable that a loss has occurred and (b) the amount of loss can be reasonably estimated. There may be instances in which an exposure to loss exceeds the accrual. We evaluate, on a quarterly basis, developments in legal proceedings that could cause an increase or decrease in the amount of the accrual that has been previously recorded, or a revision to the disclosed estimated range of possible losses, as applicable.
Derivatives	We use derivative financial instruments (derivatives) to manage exposures to various market risks. These instruments derive their value from an underlying variable or multiple variables, including interest rates, foreign exchange rates, and equity index or price, and are carried at fair value on the Consolidated Balance Sheets. The changes in the fair value of derivatives that are not designated as hedges are intended to offset the related foreign exchange gains or losses of the underlying foreign currency exposures.
Guarantees	Our recognition of these instruments is at fair value. In addition, we establish reserves when a loss is probable and the amount can be reasonably estimated.

Disclosure of accounting policy for investments in financial assets, including marketable securities (debt and equity securities with readily determinable fair values), investments accounted for under the equity method and cost method, securities borrowed and loaned, and repurchase and resale agreements. For marketable securities, the disclosure may include the entity's accounting treatment for transfers between investment categories and how the fair values for such securities are determined. Also, for all investments, an entity may describe its policy for assessing, recognizing and measuring impairment of the investment.