Investment securities (Tables)

12 Months Ended

Dec. 31, 2024

Investments, Debt and Equity Securities [Abstract]

Amortized Cost and Estimated Fair Value of Investment Securities

The amortized cost and estimated fair value of investment securities were as follows:

(Dollars in millions)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
December 31, 2024
Investment securities available for sale:
U.S. Treasury	$	7,945	$	13	$	27	$	7,931
Mortgage-backed securities:
Government issued or guaranteed:
Commercial	3,739		8		45		3,702
Residential	7,368		13		167		7,214
Other	2		—		—		2
	19,054		34		239		18,849
Investment securities held to maturity:
U.S. Treasury	1,015		—		14		1,001
Mortgage-backed securities:
Government issued or guaranteed:
Commercial	2,034		—		157		1,877
Residential	8,773		—		961		7,812
Privately issued	37		9		—		46
State and political subdivisions	2,335		—		117		2,218
Other	1		—		—		1
	14,195		9		1,249		12,955
Total debt securities	$	33,249	$	43	$	1,488	$	31,804
Equity and other securities:
Readily marketable equity — at fair value	$	235	$	3	$	3	$	235
Other — at cost	772		—		—		772
Total equity and other securities	$	1,007	$	3	$	3	$	1,007
December 31, 2023
Investment securities available for sale:
U.S. Treasury	$	7,818	$	—	$	113	$	7,705
Mortgage-backed securities:
Government issued or guaranteed:
Commercial	425		—		9		416
Residential	2,272		—		118		2,154
Other	176		—		11		165
	10,691		—		251		10,440
Investment securities held to maturity:
U.S. Treasury	1,005		—		31		974
Mortgage-backed securities:
Government issued or guaranteed:
Commercial	2,033		—		130		1,903
Residential	9,747		4		802		8,949
Privately issued	42		9		5		46
State and political subdivisions	2,501		—		67		2,434
Other	2		—		—		2
	15,330		13		1,035		14,308
Total debt securities	$	26,021	$	13	$	1,286	$	24,748
Equity and other securities:
Readily marketable equity — at fair value	$	266	$	5	$	3	$	268
Other — at cost	859		—		—		859
Total equity and other securities	$	1,125	$	5	$	3	$	1,127

Debt Securities, Held-to-Maturity, Credit Quality Indicator

As of December 31, 2024, the latest available investment ratings of obligations of states and political subdivisions, privately issued mortgage-backed securities and other debt securities were as follows:

					Average Credit Rating of Fair Value Amount
(Dollars in millions)	Amortized Cost		Estimated Fair Value		A or Better		Not Rated
State and political subdivisions	$	2,335	$	2,218	$	2,212	$	6
Privately issued mortgage-backed securities	37		46		—		46
Other	3		3		2		1

Amortized Cost and Estimated Fair Value of Debt Securities by Contractual Maturity

At December 31, 2024, the amortized cost and estimated fair value of debt securities by contractual maturity were as follows:

(Dollars in millions)	Amortized Cost		Estimated Fair Value
Debt securities available for sale:
Due in one year or less	$	2,940	$	2,929
Due after one year through five years	5,007		5,004
Due after five years through ten years	—		—
Due after ten years	—		—
	7,947		7,933
Mortgage-backed securities	11,107		10,916
	$	19,054	$	18,849
Debt securities held to maturity:
Due in one year or less	$	602	$	602
Due after one year through five years	635		618
Due after five years through ten years	1,491		1,432
Due after ten years	623		568
	3,351		3,220
Mortgage-backed securities	10,844		9,735
	$	14,195	$	12,955

Schedule of Unrealized Loss on Investments

A summary of investment securities that as of December 31, 2024 and 2023 had been in a continuous unrealized loss position for less than twelve months and those that had been in a continuous unrealized loss position for twelve months or longer follows:

	Less Than 12 Months				12 Months or More
(Dollars in millions)	Fair Value		Unrealized Losses		Fair Value		Unrealized Losses
December 31, 2024
Investment securities available for sale:
U.S. Treasury	$	1,971	$	9	$	2,554	$	18
Mortgage-backed securities:
Government issued or guaranteed:
Commercial	2,566		45		64		—
Residential	4,429		53		1,623		114
Other	—		—		2		—
	8,966		107		4,243		132
Investment securities held to maturity:
U.S. Treasury	50		—		951		14
Mortgage-backed securities:
Government issued or guaranteed:
Commercial	—		—		1,877		157
Residential	996		19		6,811		942
Privately issued	—		—		—		—
State and political subdivisions	39		1		2,131		116
	1,085		20		11,770		1,229
Total	$	10,051	$	127	$	16,013	$	1,361
December 31, 2023
Investment securities available for sale:
U.S. Treasury	$	229	$	1	$	7,474	$	112
Mortgage-backed securities:
Government issued or guaranteed:
Commercial	74		1		330		8
Residential	151		2		1,959		116
Other	6		—		154		11
	460		4		9,917		247
Investment securities held to maturity:
U.S. Treasury	50		—		924		31
Mortgage-backed securities:
Government issued or guaranteed:
Commercial	328		9		1,575		121
Residential	955		11		7,139		791
Privately issued	—		—		34		5
State and political subdivisions	218		3		2,172		64
	1,551		23		11,844		1,012
Total	$	2,011	$	27	$	21,761	$	1,259