Asset Quality - Nonperforming Assets and Past Due Loans (Parenthetical) (Detail) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Financing Receivable, Recorded Investment, Past Due [Line Items]
Purchased credit impaired loans	$ 11	$ 12	$ 11
Restructured loans	22	19	21
Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Carrying value of foreclosed residential real estate	111	116	114
Foreclosed Residential Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Carrying value of foreclosed residential real estate	$ 12	$ 15	$ 11

Purchased credit impaired loans outstanding principal balance.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

The amount of mortgage loans on real estate which were foreclosed on during the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 948
-SubTopic 310
-Section S99
-Paragraph 1
-Subparagraph (SX 210.12-29.6)
-URI http://asc.fasb.org/extlink&oid=6589523&loc=d3e617274-123014

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 10
-Section S99
-Paragraph 6
-Subparagraph (SX 210.5-04.(c) Schedule IV)
-URI http://asc.fasb.org/extlink&oid=27047687&loc=d3e5864-122674

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- Definition

Amount of restructured debt contingently payable based on the occurrence of future events or circumstances.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 60
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6402221&loc=d3e15765-112638

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