Investment Securities - Gross Unrealized Losses and Fair Value of Company's Investment Securities (Detail) $ in Millions	Mar. 31, 2022 USD ($)
Continuous Gross Unrealized Losses And Fair Value [Abstract]
Fair Value Less Than 12 Months	$ 94,661
Unrealized Losses Less Than 12 Months	(5,091)
Fair Value 12 Months or Greater	11,954
Unrealized Losses 12 Months or Greater	(1,207)
Fair Value Total	106,615
Unrealized Losses Total	(6,298)
U.S. Treasury and Agencies [Member]
Continuous Gross Unrealized Losses And Fair Value [Abstract]
Fair Value Less Than 12 Months	18,851
Unrealized Losses Less Than 12 Months	(982)
Fair Value 12 Months or Greater	3,784
Unrealized Losses 12 Months or Greater	(349)
Fair Value Total	22,635
Unrealized Losses Total	(1,331)
Residential Mortgage-Backed Securities [Member]
Continuous Gross Unrealized Losses And Fair Value [Abstract]
Fair Value Less Than 12 Months	66,323
Unrealized Losses Less Than 12 Months	(3,181)
Fair Value 12 Months or Greater	5,090
Unrealized Losses 12 Months or Greater	(405)
Fair Value Total	71,413
Unrealized Losses Total	(3,586)
Commercial Mortgage Backed Securities [Member]
Continuous Gross Unrealized Losses And Fair Value [Abstract]
Fair Value Less Than 12 Months	5,105
Unrealized Losses Less Than 12 Months	(414)
Fair Value 12 Months or Greater	2,856
Unrealized Losses 12 Months or Greater	(392)
Fair Value Total	7,961
Unrealized Losses Total	(806)
Asset-Backed Securities [Member]
Continuous Gross Unrealized Losses And Fair Value [Abstract]
Fair Value 12 Months or Greater	2
Fair Value Total	2
Obligations of State and Political Subdivisions [Member]
Continuous Gross Unrealized Losses And Fair Value [Abstract]
Fair Value Less Than 12 Months	4,378
Unrealized Losses Less Than 12 Months	(514)
Fair Value 12 Months or Greater	222
Unrealized Losses 12 Months or Greater	(61)
Fair Value Total	4,600
Unrealized Losses Total	(575)
Other [Member]
Continuous Gross Unrealized Losses And Fair Value [Abstract]
Fair Value Less Than 12 Months	4
Fair Value Total	$ 4

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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-SubTopic 30
-Section 50
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