Summary of Significant Accounting Policies and Nature of Operations	6 Months Ended
Jun. 30, 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 second 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. Beginning in 2013, fees associated with certain unused commitment balances are classified within credit facility fees in noninterest income. Such fees were previously recorded in loan interest income and totaled $13 million for the three months ended June 30, 2012 and $25 million for the six months ended June 30, 2012. The Company has corrected the prior period presentation to conform to the presentation adopted at the beginning of 2013. Recently Issued Accounting Pronouncements That Are Not Yet Effective Obligations Resulting from Joint and Several Liability Arrangements 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 on the Company's financial position or 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. Investment Companies—Amendments to the Scope, Measurement, and Disclosure Requirements In June 2013, the FASB issued ASU 2013-08, Financial Services—Investment Companies (Topic 946)—Amendments to the Scope, Measurement, and Disclosure Requirements, which changes the criteria for determining whether an entity meets the definition of an investment company, requires investment companies to measure noncontrolling ownership interests in other investment companies at fair value (rather than using the equity method of accounting), and requires additional disclosures for investment companies. This guidance is effective for interim and annual periods beginning on January 1, 2014. The revised investment company accounting must be applied to all entities that meet the new investment company definition on the effective date, with a cumulative effect adjustment to beginning retained earnings. Management is currently assessing the impact of this guidance on the Company's financial position and results of operations. Inclusion of the Fed Funds Effective Swap Rate as a Benchmark Interest Rate for Hedge Accounting Purposes In July 2013, the FASB issued ASU 2013-10, Inclusion of the Fed Funds Effective Swap Rate (or Overnight Index Swap Rate) as a Benchmark Interest Rate for Hedge Accounting Purposes, which will now permit the Fed Funds Effective Swap Rate (or Overnight Index Swap Rate) to be used as a U.S. benchmark interest rate for hedge accounting purposes. The guidance also removes the existing restriction on using different benchmark rates for similar hedge accounting relationships. This guidance is effective prospectively for qualifying new or redesignated hedging relationships entered into on or after July 17, 2013. Management does not expect the adoption of this guidance to significantly impact the Company's financial position or results of operations. Presentation of an Unrecognized Tax Benefit When a Net Operating Loss Carryforward, a Similar Tax Loss, or a Tax Credit Carryforward Exists In July 2013, the FASB issued ASU 2013-11, Presentation of an Unrecognized Tax Benefit When a Net Operating Loss Carryforward, a Similar Tax Loss, or a Tax Credit Carryforward Exists, which specifies that an unrecognized tax benefit, or a portion of an unrecognized tax benefit, should be presented as a reduction to a deferred tax asset for a net operating loss carryforward, a similar tax loss, or a tax credit carryforward. However, to the extent a net operating loss carryforward, a similar tax loss, or a tax credit carryforward is not available at the reporting date under the tax law of the applicable jurisdiction to settle any additional income taxes that would result from the disallowance of a tax position or the tax law of the applicable jurisdiction does not require the entity to use, and the entity does not intend to use, the deferred tax asset for such purpose, the unrecognized tax benefit should be presented as a liability and should not be combined with deferred tax assets. This guidance is applied prospectively beginning on January 1, 2014 to all unrecognized tax benefits that exist on that date, with retrospective application permitted. Early adoption is also 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 second 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.

Beginning in 2013, fees associated with certain unused commitment balances are classified within credit facility fees in noninterest income. Such fees were previously recorded in loan interest income and totaled $13 million for the three months ended June 30, 2012 and $25 million for the six months ended June 30, 2012. The Company has corrected the prior period presentation to conform to the presentation adopted at the beginning of 2013.

Recently Issued Accounting Pronouncements That Are Not Yet Effective

Obligations Resulting from Joint and Several Liability Arrangements 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 on the Company's financial position or 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.

Investment Companies—Amendments to the Scope, Measurement, and Disclosure Requirements

In June 2013, the FASB issued ASU 2013-08, Financial Services—Investment Companies (Topic 946)—Amendments to the Scope, Measurement, and Disclosure Requirements, which changes the criteria for determining whether an entity meets the definition of an investment company, requires investment companies to measure noncontrolling ownership interests in other investment companies at fair value (rather than using the equity method of accounting), and requires additional disclosures for investment companies. This guidance is effective for interim and annual periods beginning on January 1, 2014. The revised investment company accounting must be applied to all entities that meet the new investment company definition on the effective date, with a cumulative effect adjustment to beginning retained earnings. Management is currently assessing the impact of this guidance on the Company's financial position and results of operations.

Inclusion of the Fed Funds Effective Swap Rate as a Benchmark Interest Rate for Hedge Accounting Purposes

In July 2013, the FASB issued ASU 2013-10, Inclusion of the Fed Funds Effective Swap Rate (or Overnight Index Swap Rate) as a Benchmark Interest Rate for Hedge Accounting Purposes, which will now permit the Fed Funds Effective Swap Rate (or Overnight Index Swap Rate) to be used as a U.S. benchmark interest rate for hedge accounting purposes. The guidance also removes the existing restriction on using different benchmark rates for similar hedge accounting relationships. This guidance is effective prospectively for qualifying new or redesignated hedging relationships entered into on or after July 17, 2013. Management does not expect the adoption of this guidance to significantly impact the Company's financial position or results of operations.

Presentation of an Unrecognized Tax Benefit When a Net Operating Loss Carryforward, a Similar Tax Loss, or a Tax Credit Carryforward Exists

In July 2013, the FASB issued ASU 2013-11, Presentation of an Unrecognized Tax Benefit When a Net Operating Loss Carryforward, a Similar Tax Loss, or a Tax Credit Carryforward Exists, which specifies that an unrecognized tax benefit, or a portion of an unrecognized tax benefit, should be presented as a reduction to a deferred tax asset for a net operating loss carryforward, a similar tax loss, or a tax credit carryforward. However, to the extent a net operating loss carryforward, a similar tax loss, or a tax credit carryforward is not available at the reporting date under the tax law of the applicable jurisdiction to settle any additional income taxes that would result from the disallowance of a tax position or the tax law of the applicable jurisdiction does not require the entity to use, and the entity does not intend to use, the deferred tax asset for such purpose, the unrecognized tax benefit should be presented as a liability and should not be combined with deferred tax assets. This guidance is applied prospectively beginning on January 1, 2014 to all unrecognized tax benefits that exist on that date, with retrospective application permitted. Early adoption is also permitted. Management does not expect the adoption of this guidance to significantly impact the Company's financial position or results of operations.