Debt instrument maturities period .

No definition available.

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Namespace Prefix:	ub_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	ub_LongTermDebtTextualAbstract
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Balance Type:	na
Period Type:	duration

- Definition

Percentage of principal amount of redeemable debt under term .

+ References

No definition available.

+ Details

Name:	ub_PercentageOfPrincipalAmountOfRedeemableDebtUnderTerm
Namespace Prefix:	ub_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The stated principal amount of the debt instrument at time of issuance, which may vary from the carrying amount because of unamortized premium or discount.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 55

-Paragraph 8

-URI http://asc.fasb.org/extlink&oid=6584090&loc=d3e28878-108400

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

-Publisher AICPA

-Name Accounting Principles Board Opinion (APB)

-Number 21

-Paragraph 16, 20

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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

Name:	us-gaap_DebtInstrumentFaceAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Interest rate stated in the contractual debt agreement.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22(a)(1))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The fair value of notes issued in noncash investing and financing activities.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 50

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4332-108586

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 50

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4313-108586

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 50

-Paragraph 3

-URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4304-108586

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 32

-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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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Long-Term Debt (Details Textual) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2012	Dec. 31, 2011
Long-Term Debt (Textual) [Abstract]
Notes Issued	$ 8,000
Senior bank notes 2.125% notes due 2017 [Member]
Long-Term Debt (Textual) [Abstract]
Debt instrument, interest rate	99.699%
Aggregate Principal Amount	500
Senior bank notes 3.500% notes due 2022 [Member]
Long-Term Debt (Textual) [Abstract]
Debt instrument, interest rate	99.20%
Aggregate Principal Amount	400
Senior bank notes due on 2017 [Member]
Long-Term Debt (Textual) [Abstract]
Interest bearing rate	2.125%
Senior bank notes due on 2022 [Member]
Long-Term Debt (Textual) [Abstract]
Interest bearing rate	3.50%
Fixed rate 3.50% notes due June 2022 [Member]
Long-Term Debt (Textual) [Abstract]
Debt instrument, interest rate	3.50%
Fixed and floating rate Federal Home Loan Bank advances with maturities ranging from January 2013 to February 2016 [Member]
Long-Term Debt (Textual) [Abstract]
Debt instrument, interest rate	1.64%	1.75%
Notes Issued	$ 4,700
Floating rate notes due June 2012 [Member]
Long-Term Debt (Textual) [Abstract]
Debt instrument, interest rate	0.20%	0.76%
Floating rate notes due June 2014 [Member]
Long-Term Debt (Textual) [Abstract]
Debt instrument, interest rate	1.42%	1.48%
Fixed rate 2.125% notes due December 2013 [Member]
Long-Term Debt (Textual) [Abstract]
Debt instrument, interest rate	2.125%
Fixed rate 3.00% notes due June 2016 [Member]
Long-Term Debt (Textual) [Abstract]
Debt instrument, interest rate	3.00%
Fixed rate 6.03% notes due July 2014 (related to consolidated VIE) [Member]
Long-Term Debt (Textual) [Abstract]
Debt instrument, interest rate	6.03%
Fixed rate 5.25% notes due December 2013 [Member]
Long-Term Debt (Textual) [Abstract]
Debt instrument, interest rate	5.25%
Fixed rate 5.95% notes due May 2016 [Member]
Long-Term Debt (Textual) [Abstract]
Debt instrument, interest rate	5.95%
Fixed rate 2.125% notes due June 2017 [Member]
Long-Term Debt (Textual) [Abstract]
Debt instrument, interest rate	2.125%
Senior Subordinated Notes [Member]
Long-Term Debt (Textual) [Abstract]
Debt instrument maturities period	5 years
Senior Notes [Member]
Long-Term Debt (Textual) [Abstract]
Percentage of principal amount of redeemable debt under term	100.00%
Unsecured Debt [Member]
Long-Term Debt (Textual) [Abstract]
Debt instrument maturities period	1 year