Business Description Organization and Basis of Presentation (Policies)	6 Months Ended
	Jun. 30, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation The interim condensed consolidated financial statements have been prepared in accordance with the instructions to Form 10-Q pursuant to the rules and regulations of the U.S. Securities and Exchange Commission (“SEC”). In the opinion of management, all adjustments, consisting only of normal recurring adjustments, necessary for a fair statement of the interim results, have been made. The preparation of the condensed consolidated financial statements requires management to make certain estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the dates of the condensed consolidated financial statements and the reported amounts of revenues and expenses during the interim reporting periods. Actual results could differ from those estimates. The condensed consolidated statement of financial condition as of December 31, 2018 was derived from audited financial statements, but does not include all disclosures required by accounting principles generally accepted in the United States of America (“GAAP”).
Principles of Consolidation	Principles of Consolidation The condensed consolidated financial statements include AB and its majority-owned and/or controlled subsidiaries, and the consolidated entities that are considered to be variable interest entities (“VIEs”) and voting interest entities (“VOEs”) in which AB has a controlling financial interest. Non-controlling interests on the condensed consolidated statements of financial condition include the portion of consolidated company-sponsored investment funds in which we do not have direct equity ownership. All significant inter-company transactions and balances among the consolidated entities have been eliminated.
Reclassification	Reclassification During 2019, prior period amounts for revenues related to our middle market lending business have been reclassified from other revenues to investment advisory fees in the condensed consolidated statements of income to conform to the current period's presentation. During 2019, prior period amounts for research and miscellaneous fees related to our brokers dealers previously presented as changes in other assets are now presented as changes in receivables; and certain income taxes payable and receivable as well as deferred tax assets and liabilities previously presented as changes in payables are now presented as changes in other assets in the condensed consolidated statements of cash flows to conform to the current period's presentation.
Recently Adopted Accounting Pronouncements / Accounting Pronouncements Not Yet Adopted	Recently Adopted Accounting Pronouncements In February 2016, the Financial Accounting Standards Board ("FASB") issued ASU 2016-02, Leases. This pronouncement, along with subsequent ASUs issued to clarify certain provisions of ASU 2016-02 is now referred to as Accounting Standards Codification 842 ("ASC 842"). The standard requires a lessee to record most leases on its balance sheet while also disclosing key information about those lease arrangements. The classification criteria to distinguish between finance and operating leases are generally consistent with the classification criteria to distinguish between capital and operating leases under previous lease accounting guidance. We adopted this new standard on January 1, 2019 using the modified retrospective method. Prior comparable periods will not be adjusted under this method. We applied several practical expedients offered by ASC 842 upon adoption of this standard. These included continuing to account for existing leases based on judgments made under legacy GAAP as it relates to determining classification of leases, unamortized initial direct costs and whether contracts are leases or contain leases. We also used a practical expedient to use hindsight in determining the lease terms (using knowledge and expectations as of the standard's adoption date instead of the previous assumptions under legacy GAAP) and evaluating impairment of our right-of-use assets in the transition period (using our most up-to-date information). Adoption of this standard resulted in the recording of operating right-of-use assets and lease liabilities of $438.7 million and $574.5 million, respectively, and financing right-of-use assets and lease liabilities of $2.4 million as of January 1, 2019. The operating right-of-use assets recognized as of January 1, 2019 are net of deferred rent of $50.0 million and liabilities associated with previously recognized impairments of $85.8 million. See Note 13, Leases, for additional disclosures. In February 2018, the FASB issued ASU 2018-02, Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income, which permits a company to reclassify the disproportionate income tax effects of the 2017 Tax Cuts and Job Act ("2017 Tax Act") on items within Accumulated Other Comprehensive Income ("AOCI") to retained earnings. The FASB refers to these amounts as "stranded tax effects." The ASU also requires certain new disclosures, some of which are applicable for all companies. We adopted this standard on January 1, 2019. The adoption of this standard had no impact on our financial condition or results of operations. Accounting Pronouncements Not Yet Adopted in 2019 In June 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses (Topic 326). This new guidance relates to the accounting for credit losses on financial instruments. The new guidance introduces an approach based on expected losses to estimate credit losses on certain types of financial instruments. It also modifies the impairment model for available-for-sale debt securities and provides for a simplified accounting model for purchased financial assets with credit deterioration since their origination. The new guidance is effective for financial statements issued for fiscal years beginning after December 15, 2019, with early adoption permitted. Management currently is evaluating the impact that adoption of this standard will have on our financial condition and results of operations. In January 2017, the FASB issued ASU 2017-04, Simplifying the Test for Goodwill Impairment. The guidance removes Step 2 of the goodwill impairment test, which requires a hypothetical purchase price allocation. As a result of the revised guidance, a goodwill impairment will be the amount by which a reporting unit's carrying value exceeds its fair value, not to exceed the carrying amount of goodwill. The new guidance is effective for financial statements issued for fiscal years beginning after December 15, 2019 and will be applied prospectively. The revised guidance is not expected to have a material impact on our financial condition or results of operations. In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework-Changes to the Disclosure Requirements for Fair Value Measurement. The amendment modifies the disclosure requirements for fair value measurements by removing, modifying or adding certain disclosures. The revised guidance is effective for all companies for fiscal years beginning after December 15, 2019, and interim periods within those years. Companies are permitted to early adopt any eliminated or modified disclosure requirements and delay adoption of the additional disclosure requirements until their effective date. The removed and modified disclosures will be adopted on a retrospective basis and the new disclosures will be adopted on a prospective basis. The revised guidance is not expected to have a material impact on our financial condition or results of operations. In August 2018, the FASB issued ASU 2018-14, Compensation - Retirement Benefits - Defined Benefit Plans - General (Topic 715-20). The amendment modifies the disclosure requirements for employers that sponsor defined benefit pension or other post-retirement plans. The revised guidance is effective for financial statements issued for fiscal years ending after December 15, 2020, with early adoption permitted. The revised guidance is not expected to have a material impact on our financial condition or results of operations. Leases We determine if an arrangement is a lease at inception. Both operating and finance leases are included in the right-of-use (“ROU”) assets and lease liabilities in our condensed consolidated statement of financial condition. ROU assets represent our right to use an underlying asset for the lease term and lease liabilities represent our obligation to make lease payments arising from the lease. ROU assets and lease liabilities are recognized at commencement date based on the present value of lease payments over the lease term. We use our incremental borrowing rate based on the information available as of the date we adopted ASC 842 in determining the present value of lease payments. Our lease terms may include options to extend or terminate the lease. These options to extend or terminate are assessed on a lease-by-lease basis, and the ROU assets and lease liabilities are adjusted when it is reasonably certain that an option will be exercised. When calculating the measurement of ROU assets and lease liabilities, we utilize the fixed payments associated with the lease and do not include other variable contractual obligations, such as operating expenses, real estate taxes and employee parking. These costs are accounted for as period costs and expensed as incurred. Additionally, we exclude any intangible assets such as software licensing agreements as stated in ASC 842-10-15-1. These arrangements will continue to follow the guidance of ASC 350, Intangibles - Goodwill and Other.