BASIS OF PRESENTATION AND ACCOUNTING CHANGES (Policies)	3 Months Ended
Mar. 31, 2017
Accounting Policies [Abstract]
Accounting Changes	ACCOUNTING CHANGES Accounting for Stock-Based Compensation In March 2016, the FASB issued ASU 2016-09, Compensation—Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting in order to simplify certain complex aspects of the accounting for income taxes and forfeitures related to employee stock-based compensation. The guidance became effective for Citi beginning on January 1, 2017. Under the new standard, excess tax benefits and deficiencies related to employee stock-based compensation are recognized directly within Income tax expense or benefit in Citi’s Consolidated Statement of Income, rather than within Additional paid-in capital. The impact of this change was not material in the first quarter of 2017. The impact of this change is similarly not expected to be material for the remainder of 2017 as the majority of employees’ deferred stock-based compensation awards are granted within the first quarter of each year, and therefore vest within the first quarter of each year, commensurate with vesting in equal annual installments. For additional information on these receivables and payables, see Note 7 to the Consolidated Financial Statements in Citi’s 2016 Annual Report on Form 10-K. Additionally, as permitted under the new guidance, Citi made an accounting policy election to account for forfeitures of awards as they occur, which represents a change from the previous requirement to estimate forfeitures when recognizing compensation expense. This change resulted in a cumulative effect adjustment to retained earnings that was not material at January 1, 2017. Recognition and Measurement of Financial Assets and Financial Liabilities In January 2016, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2016-01, Financial Instruments—Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities, which addresses certain aspects of recognition, measurement, presentation and disclosure of financial instruments. This ASU requires entities to present separately in Accumulated other comprehensive income (loss) (AOCI) the portion of the total change in the fair value of a liability resulting from a change in the instrument-specific credit risk when the entity has elected to measure the liability at fair value in accordance with the fair value option for financial instruments. It also requires equity investments (except those accounted for under the equity method of accounting or those that result in consolidation of the investee) to be measured at fair value with changes in fair value recognized in net income, thus eliminating eligibility for the current available-for-sale category. However, Federal Reserve Bank and Federal Home Loan Bank stock as well as certain exchange seats will continue to be presented at cost. Citi early adopted only the provisions of this ASU related to presentation of the change in fair value of liabilities for which the fair value option was elected, related to changes in Citigroup’s own credit spreads in AOCI effective January 1, 2016. Accordingly, as of the first quarter 2016, these amounts are reflected as a component of AOCI, whereas these amounts were previously recognized in Citigroup’s revenues and net income. The impact of adopting this amendment resulted in a cumulative catch-up reclassification from retained earnings to AOCI of an accumulated after-tax loss of approximately $15 million at January 1, 2016. Financial statements for periods prior to 2016 were not subject to restatement under the provisions of this ASU. For additional information, see Note 17, Note 20 and Note 21 to the Consolidated Financial Statements. The Company is evaluating the effects that the other provisions of ASU 2016-01,which are effective on January 1, 2018, will have on its Consolidated Financial Statements and related disclosures. FUTURE APPLICATION OF ACCOUNTING STANDARDS Accounting for Financial Instruments—Credit Losses In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments—Credit Losses (Topic 326). The ASU introduces a new accounting model, the Current Expected Credit Losses model (CECL), which requires earlier recognition of credit losses, while also providing additional transparency about credit risk. The FASB’s CECL model utilizes a lifetime “expected credit loss” measurement objective for the recognition of credit losses for loans, held-to-maturity securities and other receivables at the time the financial asset is originated or acquired. The expected credit losses are adjusted each period for changes in expected lifetime credit losses. For available-for-sale securities where fair value is less than cost, credit-related impairment, if any, will be recognized in an allowance for credit losses and adjusted each period for changes in expected credit risk. This model replaces the multiple existing impairment models in current GAAP, which generally require that a loss be incurred before it is recognized. The CECL model represents a significant departure from existing GAAP and may result in material changes to the Company’s accounting for financial instruments. The Company is evaluating the effect that ASU 2016-13 will have on its Consolidated Financial Statements and related disclosures. The impact of the ASU will depend upon the state of the economy and the nature of Citi’s portfolios at the date of adoption. The ASU will be effective for Citi as of January 1, 2020. Early application is permitted for annual periods beginning January 1, 2019. Revenue Recognition In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers, which requires an entity to recognize the amount of revenue to which it expects to be entitled for the transfer of promised goods or services to customers. The Company will adopt the guidance as of January 1, 2018 with a cumulative-effect adjustment to opening retained earnings. While the guidance will replace most existing revenue recognition guidance in GAAP, the ASU is not applicable to financial instruments and, therefore, will not impact a majority of the Company’s revenue, including net interest income. While in scope of the new guidance, the Company does not expect a material change in the timing or measurement of revenues related to deposit fees. Citi’s credit cardholder fees and mortgage servicing fees have been concluded to be out of scope of the standard and therefore will not be impacted by the issuance of this guidance. The Company expects the presentation of expenses associated with underwriting activity to change from the current reporting where underwriting revenue is recorded net of the related expenses to a gross presentation where the expenses are recorded in Other operating expenses. This change to a gross presentation will result in an equivalent increase in underwriting revenue recorded in Commissions and fees and associated underwriting expenses recorded in Other operating expenses; however, this change in presentation will not have an impact on Income from continuing operations. The Company continues to evaluate the effect that the guidance will have on other revenue streams within its scope, including the presentation of certain contract expenses, as well as changes in disclosures required by the new guidance. Lease Accounting In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842), which is intended to increase transparency and comparability of accounting for lease transactions. The ASU will require lessees to recognize all leases on the balance sheet as lease assets and lease liabilities and will require both quantitative and qualitative disclosures regarding key information about leasing arrangements. Lessor accounting is largely unchanged. The guidance is effective beginning January 1, 2019 with an option to early adopt. The Company does not plan to early adopt the ASU. The Company is evaluating the effect that the standard will have on its Consolidated Financial Statements, regulatory capital and related disclosures and the impact is not expected to be material. Income Tax Impact of Intra-Entity Transfers of Assets In October 2016, the FASB issued ASU No. 2016-16, Income Taxes—Intra-Entity Transfers of Assets Other Than Inventory, which will require an entity to recognize the income tax consequences of an intra-entity transfer of an asset other than inventory when the transfer occurs. The ASU is effective on January 1, 2018 with early adoption permitted. The Company continues to evaluate the impact of this standard, which is expected to increase DTAs, with an associated decrease in prepaid taxes of approximately $500 million. Subsequent Measurement of Goodwill In January 2017, the FASB issued ASU No. 2017-04, Intangibles—Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment. The ASU simplifies the subsequent measurement of goodwill impairment by eliminating the requirement to calculate the implied fair value of goodwill (i.e., the current Step 2 of the goodwill impairment test) to measure a goodwill impairment charge. Under the ASU, the impairment test is simply the comparison of the fair value of a reporting unit with its carrying amount (the current Step 1), with the impairment charge being the deficit in fair value but not exceeding the total amount of goodwill allocated to that reporting unit. The simplified one-step impairment test applies to all reporting units (including those with zero or negative carrying amounts). The ASU is effective for Citi as of January 1, 2020. Early adoption is permitted for interim and annual goodwill impairment testing dates after January 1, 2017. The impact of the ASU will depend upon the performance of the reporting units and the market conditions impacting the fair value of each reporting unit going forward. Clarifying the Definition of a Business In January 2017, the FASB issued ASU No. 2017-01, Business Combinations (Topic 805): Clarifying the Definition of a Business. The definition of a business directly and indirectly affects many areas of accounting (e.g., acquisitions, disposals, goodwill and consolidation). The ASU narrows the definition of a business by introducing a quantitative screen as the first step, such that if substantially all of the fair value of the gross assets acquired is concentrated in a single identifiable asset or a group of similar identifiable assets, the set of transferred assets and activities is not a business. If the set is not scoped out from the quantitative screen, the entity then evaluates whether the set meets the requirement that a business include, at a minimum, an input and a substantive process that together significantly contribute to the ability to create outputs. The ASU is effective for Citi as of January 1, 2018. The ASU will be applied prospectively, with early adoption permitted. The impact of the ASU will depend upon the acquisition and disposal activities of Citi. If fewer transactions qualify as a business, there could be less initial recognition of goodwill, but also less goodwill allocated to disposals. Premiums on Purchased Callable Debt Securities In late March 2017, the FASB issued ASU No. 2017-08, Receivables—Nonrefundable Fees and Other Costs (Subtopic 310-20). The ASU changes the period of amortization of premiums on certain callable debt securities from the full contractual life of the security to the earliest call date of the security. The ASU will not change the accretion of discounts. The ASU is effective for Citi as of January 1, 2019 through a cumulative effect adjustment to retained earnings, with early adoption permitted. This accounting change will primarily affect Citi’s portfolios of available-for-sale and held-to-maturity state and municipal debt securities. The Company is evaluating the effect that the standard will have on its Consolidated Financial Statements, but based on a preliminary analysis, it is expected to result in a cumulative effect adjustment reducing retained earnings (primarily through a reclassification from AOCI) to reflect the shorter amortization period to the earliest call date for the premiums on callable debt securities. Under the new guidance, interest revenue recorded on callable bonds subject to a premium will decrease before the call date because premiums will be amortized over a shorter time period. Other Potential Amendments to Current Accounting Standards The FASB has issued a proposed ASU that will provide targeted improvements to the accounting guidance for hedging activities. The exposure draft contains many proposals for improving how the economic results of risk management are reflected in financial reporting. Specifically, among other improvements, the ASU is expected to expand the list of benchmark interest rates and also increase the ability for entities to construct hedges of interest rate risk that hedge only certain cash flows of a hedged item. If issued in its current form, the ASU is also expected to modify existing guidance related to the timing and income statement line recognition of ineffectiveness and components excluded from hedge relationships and add incremental disclosures regarding hedging activities.

ACCOUNTING CHANGES

Accounting for Stock-Based Compensation

In March 2016, the FASB issued ASU 2016-09, Compensation—Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting in order to simplify certain complex aspects of the accounting for income taxes and forfeitures related to employee stock-based compensation. The guidance became effective for Citi beginning on January 1, 2017. Under the new standard, excess tax benefits and deficiencies related to employee stock-based compensation are recognized directly within Income tax expense or benefit in Citi’s Consolidated Statement of Income, rather than within Additional paid-in capital. The impact of this change was not material in the first quarter of 2017. The impact of this change is similarly not expected to be material for the remainder of 2017 as the majority of employees’ deferred stock-based compensation awards are granted within the first quarter of each year, and therefore vest within the first quarter of each year, commensurate with vesting in equal annual installments. For additional information on these receivables and payables, see Note 7 to the Consolidated Financial Statements in Citi’s 2016 Annual Report on Form 10-K.

Additionally, as permitted under the new guidance, Citi made an accounting policy election to account for forfeitures of awards as they occur, which represents a change from the previous requirement to estimate forfeitures when recognizing compensation expense. This change resulted in a cumulative effect adjustment to retained earnings that was not material at January 1, 2017.

Recognition and Measurement of Financial Assets and Financial Liabilities

In January 2016, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2016-01, Financial Instruments—Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities, which addresses certain aspects of recognition, measurement, presentation and disclosure of financial instruments.

This ASU requires entities to present separately in Accumulated other comprehensive income (loss) (AOCI) the portion of the total change in the fair value of a liability resulting from a change in the instrument-specific credit risk when the entity has elected to measure the liability at fair value in accordance with the fair value option for financial instruments. It also requires equity investments (except those accounted for under the equity method of accounting or those that result in consolidation of the investee) to be measured at fair value with changes in fair value recognized in net income, thus eliminating eligibility for the current available-for-sale category. However, Federal Reserve Bank and Federal Home Loan Bank stock as well as certain exchange seats will continue to be presented at cost.

Citi early adopted only the provisions of this ASU related to presentation of the change in fair value of liabilities for which the fair value option was elected, related to changes in Citigroup’s own credit spreads in AOCI effective January 1, 2016. Accordingly, as of the first quarter 2016, these amounts are reflected as a component of AOCI, whereas these amounts were previously recognized in Citigroup’s revenues and net income. The impact of adopting this amendment resulted in a cumulative catch-up reclassification from retained earnings to AOCI of an accumulated after-tax loss of approximately $15 million at January 1, 2016. Financial statements for periods prior to 2016 were not subject to restatement under the provisions of this ASU. For additional information, see Note 17, Note 20 and Note 21 to the Consolidated Financial Statements. The Company is evaluating the effects that the other provisions of ASU 2016-01,which are effective on January 1, 2018, will have on its Consolidated Financial Statements and related disclosures.

FUTURE APPLICATION OF ACCOUNTING STANDARDS

Accounting for Financial Instruments—Credit Losses

In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments—Credit Losses (Topic 326). The ASU introduces a new accounting model, the Current Expected Credit Losses model (CECL), which requires earlier recognition of credit losses, while also providing additional transparency about credit risk.

The FASB’s CECL model utilizes a lifetime “expected credit loss” measurement objective for the recognition of credit losses for loans, held-to-maturity securities and other receivables at the time the financial asset is originated or acquired. The expected credit losses are adjusted each period for changes in expected lifetime credit losses. For available-for-sale securities where fair value is less than cost, credit-related impairment, if any, will be recognized in an allowance for credit losses and adjusted each period for changes in expected credit risk. This model replaces the multiple existing impairment models in current GAAP, which generally require that a loss be incurred before it is recognized.

The CECL model represents a significant departure from existing GAAP and may result in material changes to the Company’s accounting for financial instruments. The Company is evaluating the effect that ASU 2016-13 will have on its Consolidated Financial Statements and related disclosures. The impact of the ASU will depend upon the state of the economy and the nature of Citi’s portfolios at the date of adoption. The ASU will be effective for Citi as of January 1, 2020. Early application is permitted for annual periods beginning January 1, 2019.

Revenue Recognition

In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers, which requires an entity to recognize the amount of revenue to which it expects to be entitled for the transfer of promised goods or services to customers. The Company will adopt the guidance as of January 1, 2018 with a cumulative-effect adjustment to opening retained earnings. While the guidance will replace most existing revenue recognition guidance in GAAP, the ASU is not applicable to financial instruments and, therefore, will not impact a majority of the Company’s revenue, including net interest income.

While in scope of the new guidance, the Company does not expect a material change in the timing or measurement of revenues related to deposit fees. Citi’s credit cardholder fees and mortgage servicing fees have been concluded to be out of scope of the standard and therefore will not be impacted by the issuance of this guidance. The Company expects the presentation of expenses associated with underwriting activity to change from the current reporting where underwriting revenue is recorded net of the related expenses to a gross presentation where the expenses are recorded in Other operating expenses. This change to a gross presentation will result in an equivalent increase in underwriting revenue recorded in Commissions and fees and associated underwriting expenses recorded in Other operating expenses; however, this change in presentation will not have an impact on Income from continuing operations. The Company continues to evaluate the effect that the guidance will have on other revenue streams within its scope, including the presentation of certain contract expenses, as well as changes in disclosures required by the new guidance.

Lease Accounting

In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842), which is intended to increase transparency and comparability of accounting for lease transactions. The ASU will require lessees to recognize all leases on the balance sheet as lease assets and lease liabilities and will require both quantitative and qualitative disclosures regarding key information about leasing arrangements. Lessor accounting is largely unchanged. The guidance is effective beginning January 1, 2019 with an option to early adopt. The Company does not plan to early adopt the ASU. The Company is evaluating the effect that the standard will have on its Consolidated Financial Statements, regulatory capital and related disclosures and the impact is not expected to be material.

Income Tax Impact of Intra-Entity Transfers of Assets

In October 2016, the FASB issued ASU No. 2016-16, Income Taxes—Intra-Entity Transfers of Assets Other Than Inventory, which will require an entity to recognize the income tax consequences of an intra-entity transfer of an asset other than inventory when the transfer occurs. The ASU is effective on January 1, 2018 with early adoption permitted. The Company continues to evaluate the impact of this standard, which is expected to increase DTAs, with an associated decrease in prepaid taxes of approximately $500 million.

Subsequent Measurement of Goodwill

In January 2017, the FASB issued ASU No. 2017-04, Intangibles—Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment. The ASU simplifies the subsequent measurement of goodwill impairment by eliminating the requirement to calculate the implied fair value of goodwill (i.e., the current Step 2 of the goodwill impairment test) to measure a goodwill impairment charge. Under the ASU, the impairment test is simply the comparison of the fair value of a reporting unit with its carrying amount (the current Step 1), with the impairment charge being the deficit in fair value but not exceeding the total amount of goodwill allocated to that reporting unit. The simplified one-step impairment test applies to all reporting units (including those with zero or negative carrying amounts).

The ASU is effective for Citi as of January 1, 2020. Early adoption is permitted for interim and annual goodwill impairment testing dates after January 1, 2017. The impact of the ASU will depend upon the performance of the reporting units and the market conditions impacting the fair value of each reporting unit going forward.

Clarifying the Definition of a Business

In January 2017, the FASB issued ASU No. 2017-01, Business Combinations (Topic 805): Clarifying the Definition of a Business. The definition of a business directly and indirectly affects many areas of accounting (e.g., acquisitions, disposals, goodwill and consolidation). The ASU narrows the definition of a business by introducing a quantitative screen as the first step, such that if substantially all of the fair value of the gross assets acquired is concentrated in a single identifiable asset or a group of similar identifiable assets, the set of transferred assets and activities is not a business. If the set is not scoped out from the quantitative screen, the entity then evaluates whether the set meets the requirement that a business include, at a minimum, an input and a substantive process that together significantly contribute to the ability to create outputs.

The ASU is effective for Citi as of January 1, 2018. The ASU will be applied prospectively, with early adoption permitted. The impact of the ASU will depend upon the acquisition and disposal activities of Citi. If fewer transactions qualify as a business, there could be less initial recognition of goodwill, but also less goodwill allocated to disposals.

Premiums on Purchased Callable Debt Securities

In late March 2017, the FASB issued ASU No. 2017-08, Receivables—Nonrefundable Fees and Other Costs (Subtopic 310-20). The ASU changes the period of amortization of premiums on certain callable debt securities from the full contractual life of the security to the earliest call date of the security. The ASU will not change the accretion of discounts.

The ASU is effective for Citi as of January 1, 2019 through a cumulative effect adjustment to retained earnings, with early adoption permitted. This accounting change will primarily affect Citi’s portfolios of available-for-sale and held-to-maturity state and municipal debt securities. The Company is evaluating the effect that the standard will have on its Consolidated Financial Statements, but based on a preliminary analysis, it is expected to result in a cumulative effect adjustment reducing retained earnings (primarily through a reclassification from AOCI) to reflect the shorter amortization period to the earliest call date for the premiums on callable debt securities. Under the new guidance, interest revenue recorded on callable bonds subject to a premium will decrease before the call date because premiums will be amortized over a shorter time period.

Other Potential Amendments to Current Accounting Standards

The FASB has issued a proposed ASU that will provide targeted improvements to the accounting guidance for hedging activities. The exposure draft contains many proposals for improving how the economic results of risk management are reflected in financial reporting. Specifically, among other improvements, the ASU is expected to expand the list of benchmark interest rates and also increase the ability for entities to construct hedges of interest rate risk that hedge only certain cash flows of a hedged item. If issued in its current form, the ASU is also expected to modify existing guidance related to the timing and income statement line recognition of ineffectiveness and components excluded from hedge relationships and add incremental disclosures regarding hedging activities.