Additional Amortization Expense Related To Fair Value Adjustments And Liabilities Assumed

No definition available.

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- Details

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- Definition

Business Acquisition Loans Receivable Acquired, Contractual Amounts Due

+ References

No definition available.

+ Details

Name:	ub_BusinessAcquisitionLoansReceivableAcquiredContractualAmountsDue
Namespace Prefix:	ub_
Data Type:	xbrli:monetaryItemType
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- Definition

Business Acquisition Purchase Price Allocation Deposits

+ References

No definition available.

+ Details

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- Definition

Business Acquisition Purchase Price Allocation Loans

+ References

No definition available.

+ Details

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- Definition

Business Acquisition Purchase Price Allocation Securities

+ References

No definition available.

+ Details

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- Definition

Business Acquisition Purchase Price Allocation Short Term Borrowings

+ References

No definition available.

+ Details

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- Definition

Business Acquisition Purchase Price Fair Value Adjustment Increase Decrease Loans Acquired

+ References

No definition available.

+ Details

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- Definition

Amount of cash paid to acquire the entity.

+ References

+ Details

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- Definition

The amount of acquisition cost of a business combination allocated to assets acquired.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 141

-Paragraph 37

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

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- Definition

The amount of acquisition cost of a business combination allocated to the current portion of long-term debt of the acquired entity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 141

-Paragraph 51

-Subparagraph e

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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- Definition

For receivables acquired in a business combination, excluding certain loans and debt securities acquired in a transfer (as defined), this element represents the best estimate at the acquisition date of the contractual cash flows not expected to be collected, by major class of receivable, such as loans, direct finance leases (as defined), and any other class of receivables.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 141R

-Paragraph 68

-Subparagraph h(3)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Statement of Position (SOP)

-Number 03-3

-Paragraph 3

-Subparagraph a-g

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 13

-Paragraph 6

-Subparagraph b(ii)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (b)(3)

-URI http://asc.fasb.org/extlink&oid=6910749&loc=d3e4845-128472

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- Definition

This element represents acquisition-related costs incurred to effect a business combination which costs have been expensed during the period. Such costs include finder's fees; advisory, legal, accounting, valuation, and other professional or consulting fees; general administrative costs, including the costs of maintaining an internal acquisitions department; and may include costs of registering and issuing debt and equity securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 10

-Section 25

-Paragraph 23

-URI http://asc.fasb.org/extlink&oid=21917927&loc=d3e1043-128460

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 141R

-Paragraph 59

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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Business Combinations - Additional Information (Detail) (USD $)	12 Months Ended					12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 01, 2012	Apr. 16, 2010 Tamalpais Bank [Member]	Apr. 30, 2010 Frontier [Member]	Dec. 31, 2012 Union Ban Cal Corporation [Member]	Dec. 31, 2012 PC Bancorp [Member]
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items]
Business acquisition cash paid			$ 1,500,000,000
Acquisition of assets at fair value			6,719,000,000	572,000,000	2,900,000,000
Acquired loans			3,795,000,000
Acquired securities available for sale			1,196,000,000
Deposits			4,670,000,000
Other short-term borrowings			313,000,000
Long-term debt and other borrowings			87,000,000
Fair value of loans, totaled			3,000,000,000
Contractual amounts receivable, totaled			3,600,000,000
Expected uncollectible loans			159,000,000
Additional amortization expenses related to fair value adjustments	31,000,000	37,000,000
Acquisition-related costs	$ 74,000,000					$ 48,000,000	$ 26,000,000