Mortgage Servicing Rights - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Transfers and Servicing of Financial Assets [Abstract]
Residential mortgage loans serviced for others including subserviced mortgages with no corresponding MSRs asset	$ 220,300		$ 220,300		$ 226,000
Gain (Loss) on fair value changes of MSRs due to changes in valuation assumptions and derivatives used to economically hedge MSRs	24	$ (14)	49	$ (3)
Loan servicing and ancillary fees	$ 174	$ 180	$ 360	$ 359

Amount of contractually specified servicing fee, late fee, and ancillary fee recognized as income for servicing asset and servicing liability.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=116651436&loc=d3e122596-111746

Name:	us-gaap_ContractuallySpecifiedServicingFeesLateFeesAndAncillaryFeesEarnedInExchangeForServicingFinancialAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration