Fair Values of Assets and Liabilities - Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2025	Mar. 31, 2024	Dec. 31, 2024	Dec. 31, 2023
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	[1]	$ 86,774		$ 85,992
Mortgage loans held for sale		1,704		2,251
Mortgage servicing rights		3,312	$ 3,462	3,369	$ 3,377
Derivative assets netting		(2,680)		(2,979)
Time deposits		6,506		5,754
Long-term debt		645		391
Derivative liabilities netting		(2,835)		(2,949)
Equity investments without readily determinable fair values		166		159
Equity investments without readily determinable fair values impairment loss cumulative amount		0		0
Equity investments without readily determinable fair values impairment loss		0	$ 0
U.S. Treasury and agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		28,616		28,387
Residential mortgage-backed securities | Agency
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		33,674		33,281
Commercial mortgage-backed securities | Agency
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		7,503		7,351
Commercial mortgage-backed securities | Non-agency
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		7		6
Asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		7,332		7,165
Obligations of state and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		9,326		9,552
Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		316		250
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		86,774		85,992
Mortgage loans held for sale		1,704		2,251
Mortgage servicing rights		3,312		3,369
Derivative assets netting		(2,680)		(2,979)
Derivative assets		3,270		3,458
Other assets		2,767		2,189
Total assets		97,827		97,259
Time deposits		6,506		5,754
Long-term debt		645		391
Derivative liabilities netting		(2,835)		(2,949)
Derivative liabilities		3,928		5,211
Short-term borrowings and other liabilities		2,446		1,935
Total liabilities		13,525		13,291
Fair Value, Measurements, Recurring | U.S. Treasury and agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		28,616		28,387
Fair Value, Measurements, Recurring | Residential mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		33,674		33,281
Fair Value, Measurements, Recurring | Commercial mortgage-backed securities | Agency
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		7,503		7,351
Fair Value, Measurements, Recurring | Commercial mortgage-backed securities | Non-agency
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		7		6
Fair Value, Measurements, Recurring | Asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		7,332		7,165
Fair Value, Measurements, Recurring | Obligations of state and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		9,326		9,552
Fair Value, Measurements, Recurring | Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		316		250
Fair Value, Measurements, Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		23,999		23,891
Mortgage loans held for sale		0		0
Mortgage servicing rights		0		0
Derivative assets before netting		53		27
Other assets		434		420
Total assets		24,486		24,338
Time deposits		0		0
Long-term debt		0		0
Derivative liabilities before netting		84		27
Short-term borrowings and other liabilities		587		475
Total liabilities		671		502
Fair Value, Measurements, Recurring | Level 1 | U.S. Treasury and agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		23,999		23,891
Fair Value, Measurements, Recurring | Level 1 | Residential mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		0		0
Fair Value, Measurements, Recurring | Level 1 | Commercial mortgage-backed securities | Agency
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		0		0
Fair Value, Measurements, Recurring | Level 1 | Commercial mortgage-backed securities | Non-agency
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		0		0
Fair Value, Measurements, Recurring | Level 1 | Asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		0		0
Fair Value, Measurements, Recurring | Level 1 | Obligations of state and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		0		0
Fair Value, Measurements, Recurring | Level 1 | Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		0		0
Fair Value, Measurements, Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		62,775		62,101
Mortgage loans held for sale		1,704		2,251
Mortgage servicing rights		0		0
Derivative assets before netting		4,374		5,208
Other assets		2,333		1,769
Total assets		71,186		71,329
Time deposits		6,506		5,754
Long-term debt		645		391
Derivative liabilities before netting		4,429		5,131
Short-term borrowings and other liabilities		1,859		1,460
Total liabilities		13,439		12,736
Fair Value, Measurements, Recurring | Level 2 | U.S. Treasury and agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		4,617		4,496
Fair Value, Measurements, Recurring | Level 2 | Residential mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		33,674		33,281
Fair Value, Measurements, Recurring | Level 2 | Commercial mortgage-backed securities | Agency
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		7,503		7,351
Fair Value, Measurements, Recurring | Level 2 | Commercial mortgage-backed securities | Non-agency
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		7		6
Fair Value, Measurements, Recurring | Level 2 | Asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		7,332		7,165
Fair Value, Measurements, Recurring | Level 2 | Obligations of state and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		9,326		9,552
Fair Value, Measurements, Recurring | Level 2 | Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		316		250
Fair Value, Measurements, Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		0		0
Mortgage loans held for sale		0		0
Mortgage servicing rights		3,312		3,369
Derivative assets before netting		1,523		1,202
Other assets		0		0
Total assets		4,835		4,571
Time deposits		0		0
Long-term debt		0		0
Derivative liabilities before netting		2,250		3,002
Short-term borrowings and other liabilities		0		0
Total liabilities		2,250		3,002
Fair Value, Measurements, Recurring | Level 3 | U.S. Treasury and agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		0		0
Fair Value, Measurements, Recurring | Level 3 | Residential mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		0		0
Fair Value, Measurements, Recurring | Level 3 | Commercial mortgage-backed securities | Agency
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		0		0
Fair Value, Measurements, Recurring | Level 3 | Commercial mortgage-backed securities | Non-agency
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		0		0
Fair Value, Measurements, Recurring | Level 3 | Asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		0		0
Fair Value, Measurements, Recurring | Level 3 | Obligations of state and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		0		0
Fair Value, Measurements, Recurring | Level 3 | Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		$ 0		$ 0

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