Asset Quality - Nonperforming Assets and Past Due Loans (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended	12 Months Ended
Sep. 30, 2012	Dec. 31, 2012	Sep. 30, 2013
Receivables [Abstract]
Performing home equity second liens including nonperforming loans	$ 38	$ 72
Purchased credit impaired loans	25	23	18
Restructured loans	$ 3	$ 3	$ 11

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

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

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 15

-Paragraph 26

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant