Summary of Significant Accounting Policies and Nature of Operations	3 Months Ended
Mar. 31, 2013
Accounting Policies [Abstract]
Summary of Significant Accounting Policies and Nature of Operations	Note 1—Summary of Significant Accounting Policies and Nature of Operations The unaudited consolidated financial statements of UnionBanCal Corporation, its subsidiaries, and its consolidated variable interest entities (the Company) have been prepared in accordance with accounting principles generally accepted in the United States of America (U.S. GAAP) for interim financial reporting and the instructions to Form 10-Q and Rule 10-01 of Regulation S-X of the Rules and Regulations of the Securities and Exchange Commission (SEC). However, they do not include all of the disclosures necessary for annual financial statements. In the opinion of management, all adjustments, consisting of normal recurring accruals, considered necessary for a fair presentation have been included. The results of operations for the first quarter of 2013 are not necessarily indicative of the operating results anticipated for the full year. These unaudited consolidated financial statements should be read in conjunction with the audited consolidated financial statements included in UnionBanCal Corporation’s Annual Report on Form 10-K for the year ended December 31, 2012 (2012 Form 10-K). The preparation of financial statements in conformity with U.S. GAAP also requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenue and expense during the reporting period. Although such estimates contemplate current conditions and management’s expectations of how they may change in the future, it is reasonably possible that actual results could differ significantly from those estimates. This could materially affect the Company’s results of operations and financial condition in the near term. Significant estimates made by management in the preparation of the Company’s financial statements include, but are not limited to, the evaluation of other-than-temporary impairment on investment securities (Note 3), allowance for credit losses (Note 4), purchased credit-impaired loans (Note 4), annual goodwill impairment analysis, pension accounting (Note 6), fair value of financial instruments (Note 9), and income taxes. UnionBanCal Corporation is a financial holding company and bank holding company whose principal subsidiary is Union Bank, N.A. (the Bank). The Company provides a wide range of financial services to consumers, small businesses, middle-market companies and major corporations, primarily in California, Oregon, Washington, Texas, New York, and Illinois, as well as nationally and internationally. During the first quarter of 2013, fees based on certain unused commitment balances are classified within credit facility fees. These fees were previously recorded in net interest income and totaled $12 million for the quarter ended March 31, 2012. Recently Issued Accounting Pronouncements That Are Not Yet Effective Obligations Resulting from Joint and Several Liability Arrangement for Which the Total Amount of the Obligation Is Fixed at the Reporting Date In February 2013, the FASB issued ASU 2013-04, Obligations Resulting from Joint and Several Liability Arrangements for Which the Total Amount of the Obligation Is Fixed at the Reporting Date, which provides guidance for the recognition, measurement, and disclosure of obligations resulting from joint and several liability arrangements for which the total amount of the obligation is fixed at the reporting date. Examples of obligations within the scope of this guidance include debt arrangements, other contractual obligations, and settled litigation and judicial rulings. This guidance is effective for interim and annual periods beginning on January 1, 2014 and must be retroactively applied to prior periods presented. Early adoption is permitted. Management is currently assessing the impact of this guidance to the Company’s financial position and results of operations. Parent’s Accounting for the Cumulative Translation Adjustment upon Derecognition of Certain Subsidiaries or Groups of Assets within a Foreign Entity or of an Investment in a Foreign Entity In March 2013, the FASB issued ASU 2013-05, Parent’s Accounting for the Cumulative Translation Adjustment upon Derecognition of Certain Subsidiaries or Groups of Assets within a Foreign Entity or of an Investment in a Foreign Entity, which provides guidance on releasing cumulative translation adjustments out of accumulated comprehensive income when a parent deconsolidates or derecognizes a subsidiary or group of assets that is a not for profit activity or a business within a foreign entity or deconsolidates or derecognizes investments in a foreign entity. This guidance is effective prospectively for interim and annual periods beginning on January 1, 2014. Early adoption is permitted. Management does not expect the adoption of this guidance to significantly impact the Company’s financial position or results of operations.

Note 1—Summary of Significant Accounting Policies and Nature of Operations

The unaudited consolidated financial statements of UnionBanCal Corporation, its subsidiaries, and its consolidated variable interest entities (the Company) have been prepared in accordance with accounting principles generally accepted in the United States of America (U.S. GAAP) for interim financial reporting and the instructions to Form 10-Q and Rule 10-01 of Regulation S-X of the Rules and Regulations of the Securities and Exchange Commission (SEC). However, they do not include all of the disclosures necessary for annual financial statements. In the opinion of management, all adjustments, consisting of normal recurring accruals, considered necessary for a fair presentation have been included. The results of operations for the first quarter of 2013 are not necessarily indicative of the operating results anticipated for the full year. These unaudited consolidated financial statements should be read in conjunction with the audited consolidated financial statements included in UnionBanCal Corporation’s Annual Report on Form 10-K for the year ended December 31, 2012 (2012 Form 10-K).

The preparation of financial statements in conformity with U.S. GAAP also requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenue and expense during the reporting period. Although such estimates contemplate current conditions and management’s expectations of how they may change in the future, it is reasonably possible that actual results could differ significantly from those estimates. This could materially affect the Company’s results of operations and financial condition in the near term. Significant estimates made by management in the preparation of the Company’s financial statements include, but are not limited to, the evaluation of other-than-temporary impairment on investment securities (Note 3), allowance for credit losses (Note 4), purchased credit-impaired loans (Note 4), annual goodwill impairment analysis, pension accounting (Note 6), fair value of financial instruments (Note 9), and income taxes.

UnionBanCal Corporation is a financial holding company and bank holding company whose principal subsidiary is Union Bank, N.A. (the Bank). The Company provides a wide range of financial services to consumers, small businesses, middle-market companies and major corporations, primarily in California, Oregon, Washington, Texas, New York, and Illinois, as well as nationally and internationally.

During the first quarter of 2013, fees based on certain unused commitment balances are classified within credit facility fees. These fees were previously recorded in net interest income and totaled $12 million for the quarter ended March 31, 2012.

Recently Issued Accounting Pronouncements That Are Not Yet Effective

Obligations Resulting from Joint and Several Liability Arrangement for Which the Total Amount of the Obligation Is Fixed at the Reporting Date

In February 2013, the FASB issued ASU 2013-04, Obligations Resulting from Joint and Several Liability Arrangements for Which the Total Amount of the Obligation Is Fixed at the Reporting Date, which provides guidance for the recognition, measurement, and disclosure of obligations resulting from joint and several liability arrangements for which the total amount of the obligation is fixed at the reporting date. Examples of obligations within the scope of this guidance include debt arrangements, other contractual obligations, and settled litigation and judicial rulings. This guidance is effective for interim and annual periods beginning on January 1, 2014 and must be retroactively applied to prior periods presented. Early adoption is permitted. Management is currently assessing the impact of this guidance to the Company’s financial position and results of operations.

Parent’s Accounting for the Cumulative Translation Adjustment upon Derecognition of Certain Subsidiaries or Groups of Assets within a Foreign Entity or of an Investment in a Foreign Entity

In March 2013, the FASB issued ASU 2013-05, Parent’s Accounting for the Cumulative Translation Adjustment upon Derecognition of Certain Subsidiaries or Groups of Assets within a Foreign Entity or of an Investment in a Foreign Entity, which provides guidance on releasing cumulative translation adjustments out of accumulated comprehensive income when a parent deconsolidates or derecognizes a subsidiary or group of assets that is a not for profit activity or a business within a foreign entity or deconsolidates or derecognizes investments in a foreign entity. This guidance is effective prospectively for interim and annual periods beginning on January 1, 2014. Early adoption is permitted. Management does not expect the adoption of this guidance to significantly impact the Company’s financial position or results of operations.