Investment Securities - Gross Unrealized Losses and Fair Value of Company's Investment Securities (Detail) $ in Millions	Sep. 30, 2022 USD ($)
Continuous Gross Unrealized Losses And Fair Value [Abstract]
Fair Value Less Than 12 Months	$ 52,003
Unrealized Losses Less Than 12 Months	(5,697)
Fair Value 12 Months or Greater	15,272
Unrealized Losses 12 Months or Greater	(3,544)
Fair Value Total	67,275
Unrealized Losses Total	(9,241)
U.S. Treasury and Agencies [Member]
Continuous Gross Unrealized Losses And Fair Value [Abstract]
Fair Value Less Than 12 Months	16,648
Unrealized Losses Less Than 12 Months	(1,870)
Fair Value 12 Months or Greater	4,831
Unrealized Losses 12 Months or Greater	(1,014)
Fair Value Total	21,479
Unrealized Losses Total	(2,884)
Residential Mortgage-Backed Securities [Member]
Continuous Gross Unrealized Losses And Fair Value [Abstract]
Fair Value Less Than 12 Months	24,355
Unrealized Losses Less Than 12 Months	(1,787)
Fair Value 12 Months or Greater	5,377
Unrealized Losses 12 Months or Greater	(966)
Fair Value Total	29,732
Unrealized Losses Total	(2,753)
Commercial Mortgage Backed Securities [Member]
Continuous Gross Unrealized Losses And Fair Value [Abstract]
Fair Value Less Than 12 Months	2,992
Unrealized Losses Less Than 12 Months	(559)
Fair Value 12 Months or Greater	4,100
Unrealized Losses 12 Months or Greater	(1,096)
Fair Value Total	7,092
Unrealized Losses Total	(1,655)
Obligations of State and Political Subdivisions [Member]
Continuous Gross Unrealized Losses And Fair Value [Abstract]
Fair Value Less Than 12 Months	8,006
Unrealized Losses Less Than 12 Months	(1,481)
Fair Value 12 Months or Greater	960
Unrealized Losses 12 Months or Greater	(468)
Fair Value Total	8,966
Unrealized Losses Total	(1,949)
Other [Member]
Continuous Gross Unrealized Losses And Fair Value [Abstract]
Fair Value Less Than 12 Months	2
Fair Value 12 Months or Greater	4
Fair Value Total	$ 6