Mortgage Servicing Rights - Changes in Fair Value of Capitalized MSRs (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Transfers and Servicing of Financial Assets [Abstract]
Balance at beginning of period	$ 2,680us-gaap_ServicingAssetAtFairValueAmount	$ 1,700us-gaap_ServicingAssetAtFairValueAmount	$ 1,519us-gaap_ServicingAssetAtFairValueAmount
Rights purchased	5	8	42
Rights capitalized	382	769	957
Rights sold	(141)
Changes in fair value of MSRs
Due to fluctuations in market interest rates	(276)	617	(249)
Due to revised assumptions or models	86	33	(21)
Other changes in fair value	(398)	(447)	(548)
Balance at end of period	$ 2,338us-gaap_ServicingAssetAtFairValueAmount	$ 2,680us-gaap_ServicingAssetAtFairValueAmount	$ 1,700us-gaap_ServicingAssetAtFairValueAmount

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Servicing asset at fair value changes in fair value resulting from fluctuations in market interest rates.

+ References

No definition available.

+ Details

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- Definition

Servicing asset at fair value rights capitalized.

+ References

No definition available.

+ Details

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- Definition

The net increase or decrease in fair value as a result of changes in the assumptions or model used to calculate the fair value of servicing assets.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 50

-Section 50

-Paragraph 3

-Subparagraph (a)(4)(i)

-URI http://asc.fasb.org/extlink&oid=7882072&loc=d3e122625-111746

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- Definition

The value of new servicing assets, subsequently measured at fair value, acquired or created during the current period through purchases or from transfers of financial assets.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 50

-Section 50

-Paragraph 3

-Subparagraph (a)(2)

-URI http://asc.fasb.org/extlink&oid=7882072&loc=d3e122625-111746

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- Definition

Fair value of an asset representing net future revenue from contractually specified servicing fees, late charges, and other ancillary revenues, in excess of future costs related to servicing arrangements.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 50

-Section 50

-Paragraph 3

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=7882072&loc=d3e122625-111746

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- Definition

Decrease in servicing assets subsequently measured at fair value resulting from conveyance of servicing rights to unrelated parties.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 50

-Section 50

-Paragraph 3

-Subparagraph (a)(3)

-URI http://asc.fasb.org/extlink&oid=7882072&loc=d3e122625-111746

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- Definition

The net Increase or Decrease in fair value as a result of other changes that are not additions, disposals, or a result of change in the inputs, assumptions, or model used to calculate the fair value of servicing assets.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 50

-Section 50

-Paragraph 3

-Subparagraph (a)(4)(ii)

-URI http://asc.fasb.org/extlink&oid=7882072&loc=d3e122625-111746

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