Commitments (Risk Rating Under the Risk Rating System) (Detail) - Commitments to Extend Credit - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Line of Credit Facility
Commitments	$ 68,089	$ 68,106
Pass
Line of Credit Facility
Commitments	67,323	67,254
Special Mention
Line of Credit Facility
Commitments	354	330
Substandard
Line of Credit Facility
Commitments	412	522
Doubtful
Line of Credit Facility
Commitments	$ 0	$ 0

Fair value portion of arrangements with third parties, including, but not limited to, operating lease arrangement and arrangement in which the entity has agreed to expend funds to procure goods or services, or has agreed to commit resources to supply goods or services.

Reference 1: 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(25))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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