Commitments (Standby and Commercial Letters of Credit, Conditional Commitments Issued to Guarantee the Performance of a Customer to a Third Party) (Detail) - Letters of Credit $ in Millions	Dec. 31, 2019 USD ($)
Line of Credit Facility
Commitments	$ 2,137
Less Than One Year From The Balance Sheet Date
Line of Credit Facility
Commitments	1,022
More than One and within Five Years from Balance Sheet Date
Line of Credit Facility
Commitments	1,110
More than Five Years from Balance Sheet Date
Line of Credit Facility
Commitments	$ 5

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://fasb.org/us-gaap/role/ref/legacyRef
-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