Credit Quality (Credit Quality Additional Information) (Detail) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Troubled Debt Restructuring
Line of credit commitments for modified troubled debt restructurings	$ 87	$ 39
Letter of credit commitments for modified troubled debt restructurings	58	23
Mortgage loans in process of foreclosure amount	$ 264	$ 303

Recorded investment of consumer mortgage loan receivables secured by residential real estate properties for which formal foreclosure proceedings are in process.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 35
-URI http://asc.fasb.org/extlink&oid=49124121&loc=SL49126937-111524

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant