Investment Securities - Gross Unrealized Losses and Fair Value of Company's Investment Securities (Detail) $ in Millions	Jun. 30, 2021 USD ($)
Continuous Gross Unrealized Losses And Fair Value [Abstract]
Fair Value Less Than 12 Months	$ 70,703
Unrealized Losses Less Than 12 Months	(1,239)
Fair Value 12 Months or Greater	157
Unrealized Losses 12 Months or Greater	(5)
Fair Value Total	70,860
Unrealized Losses Total	(1,244)
U.S. Treasury and Agencies [Member]
Continuous Gross Unrealized Losses And Fair Value [Abstract]
Fair Value Less Than 12 Months	8,922
Unrealized Losses Less Than 12 Months	(232)
Fair Value Total	8,922
Unrealized Losses Total	(232)
Residential Mortgage-Backed Securities [Member]
Continuous Gross Unrealized Losses And Fair Value [Abstract]
Fair Value Less Than 12 Months	57,626
Unrealized Losses Less Than 12 Months	(909)
Fair Value 12 Months or Greater	148
Unrealized Losses 12 Months or Greater	(4)
Fair Value Total	57,774
Unrealized Losses Total	(913)
Commercial Mortgage Backed Securities [Member]
Continuous Gross Unrealized Losses And Fair Value [Abstract]
Fair Value Less Than 12 Months	3,285
Unrealized Losses Less Than 12 Months	(91)
Fair Value 12 Months or Greater	6
Fair Value Total	3,291
Unrealized Losses Total	(91)
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	870
Unrealized Losses Less Than 12 Months	(7)
Fair Value 12 Months or Greater	1
Unrealized Losses 12 Months or Greater	(1)
Fair Value Total	871
Unrealized Losses Total	$ (8)

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.

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