Fair Values of Assets and Liabilities - Balances of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Millions		Sep. 30, 2023		Jun. 30, 2023	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Dec. 31, 2021
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities netting		$ (4,307)			$ (4,551)
Derivative assets netting		(4,515)			(5,427)
Available-for-sale securities	[2]	67,207	[1],[3]		72,910
Mortgage loans held for sale		2,263			1,849
Mortgage servicing rights		3,582		$ 3,633	3,755	$ 3,869	$ 3,707	$ 2,953
Time deposits		444			0
Residential Mortgage-Backed Securities [Member] | Agency [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		25,614			29,271
Commercial Mortgage-Backed Securities [Member] | Agency [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		6,942			7,145
Commercial Mortgage-Backed Securities [Member] | Non Agency [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		6			7
Asset-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		6,868	[4]		4,323
Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		4			6
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities total		7,514			6,148
Derivative assets total		3,122			2,445
Available-for-sale securities		67,207			72,910
Mortgage loans held for sale		2,263			1,849
Mortgage servicing rights		3,582			3,755
Other assets		2,412			2,004
Total		78,586			82,963
Short-term borrowings and other liabilities		1,953			1,689
Total		9,911			7,837
Fair Value, Measurements, Recurring [Member] | Time Deposits [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Time deposits		444
Fair Value, Measurements, Recurring [Member] | Netting and Collateral One [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities netting		(4,307)			(4,551)
Derivative assets netting		(4,515)			(5,427)
Available-for-sale securities		0			0
Mortgage loans held for sale		0			0
Mortgage servicing rights		0			0
Other assets		0			0
Total		(4,515)			(5,427)
Short-term borrowings and other liabilities		0			0
Total		(4,307)			(4,551)
Fair Value, Measurements, Recurring [Member] | Netting and Collateral One [Member] | Time Deposits [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Time deposits		0
Fair Value, Measurements, Recurring [Member] | U.S. Treasury and Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		18,707			22,033
Fair Value, Measurements, Recurring [Member] | U.S. Treasury and Agencies [Member] | Netting and Collateral One [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		0			0
Fair Value, Measurements, Recurring [Member] | Obligations of State and Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		9,066			10,125
Fair Value, Measurements, Recurring [Member] | Obligations of State and Political Subdivisions [Member] | Netting and Collateral One [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		0			0
Fair Value, Measurements, Recurring [Member] | Residential Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		25,614			29,271
Fair Value, Measurements, Recurring [Member] | Residential Mortgage-Backed Securities [Member] | Netting and Collateral One [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		0			0
Fair Value, Measurements, Recurring [Member] | Commercial Mortgage-Backed Securities [Member] | Agency [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		6,942			7,145
Fair Value, Measurements, Recurring [Member] | Commercial Mortgage-Backed Securities [Member] | Agency [Member] | Netting and Collateral One [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		0			0
Fair Value, Measurements, Recurring [Member] | Commercial Mortgage-Backed Securities [Member] | Non Agency [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		6			7
Fair Value, Measurements, Recurring [Member] | Commercial Mortgage-Backed Securities [Member] | Non Agency [Member] | Netting and Collateral One [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		0			0
Fair Value, Measurements, Recurring [Member] | Asset-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		6,868			4,323
Fair Value, Measurements, Recurring [Member] | Asset-Backed Securities [Member] | Netting and Collateral One [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		0			0
Fair Value, Measurements, Recurring [Member] | Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		4			6
Fair Value, Measurements, Recurring [Member] | Other [Member] | Netting and Collateral One [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		0			0
Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities before netting		0			4
Derivative assets before netting		4			9
Available-for-sale securities		14,112			13,723
Mortgage loans held for sale		0			0
Mortgage servicing rights		0			0
Other assets		406			248
Total		14,522			13,980
Short-term borrowings and other liabilities		309			125
Total		309			129
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Time Deposits [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Time deposits		0
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | U.S. Treasury and Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		14,112			13,723
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Obligations of State and Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		0			0
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Residential Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		0			0
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Commercial Mortgage-Backed Securities [Member] | Agency [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		0			0
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Commercial Mortgage-Backed Securities [Member] | Non Agency [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		0			0
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Asset-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		0			0
Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		0			0
Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities before netting		6,685			6,241
Derivative assets before netting		6,253			6,608
Available-for-sale securities		53,095			59,186
Mortgage loans held for sale		2,263			1,849
Mortgage servicing rights		0			0
Other assets		2,006			1,756
Total		63,617			69,399
Short-term borrowings and other liabilities		1,644			1,564
Total		8,773			7,805
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Time Deposits [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Time deposits		444
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | U.S. Treasury and Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		4,595			8,310
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Obligations of State and Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		9,066			10,124
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Residential Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		25,614			29,271
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Commercial Mortgage-Backed Securities [Member] | Agency [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		6,942			7,145
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Commercial Mortgage-Backed Securities [Member] | Non Agency [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		6			7
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Asset-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		6,868			4,323
Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		4			6
Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities before netting		5,136			4,454
Derivative assets before netting		1,380			1,255
Available-for-sale securities		0			1
Mortgage loans held for sale		0			0
Mortgage servicing rights		3,582			3,755
Other assets		0			0
Total		4,962			5,011
Short-term borrowings and other liabilities		0			0
Total		5,136			4,454
Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Time Deposits [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Time deposits		0
Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | U.S. Treasury and Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		0			0
Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Obligations of State and Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		0			1
Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Residential Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		0			0
Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Commercial Mortgage-Backed Securities [Member] | Agency [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		0			0
Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Commercial Mortgage-Backed Securities [Member] | Non Agency [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		0			0
Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Asset-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		0			0
Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		$ 0			$ 0

[1] Amortized cost excludes portfolio level basis adjustments of $(95) million.

[2] Includes only collateral pledged by the Company where counterparties have the right to sell or pledge the collateral.

[3] The weighted-average maturity of total held-to-maturity investment securities was 9.2 years at December 31, 2022, with a corresponding weighted-average yield of 2.18 percent. The weighted-average maturity of total available-for-sale investment securities was 7.4 years at December 31, 2022, with a corresponding weighted-average yield of 2.94 percent.

[4] Information related to asset and mortgage-backed securities included above is presented based upon weighted-average maturities that take into account anticipated future prepayments.