Credit Quality (Credit Quality Additional Information) (Detail) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Troubled Debt Restructuring
Line of credit commitments for modified troubled debt restructurings	$ 45	$ 41
Letter of credit commitments for modified troubled debt restructurings	66	58
Mortgage loans in process of foreclosure amount	$ 181	$ 212

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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 35
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL49126937-111524

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