Investment securities (Tables)

9 Months Ended

Sep. 30, 2023

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:

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
	(In thousands)
September 30, 2023
Investment securities available for sale:
U.S. Treasury and federal agencies	$	7,935,658	$	—	$	200,551	$	7,735,107
Mortgage-backed securities:
Government issued or guaranteed:
Commercial		544,263		—		18,794		525,469
Residential		2,382,810		8		214,531		2,168,287
Other debt securities		176,235		146		12,835		163,546
		11,038,966		154		446,711		10,592,409
Investment securities held to maturity:
U.S. Treasury and federal agencies		1,001,991		—		48,706		953,285
Obligations of states and political subdivisions		2,511,784		—		219,149		2,292,635
Mortgage-backed securities:
Government issued or guaranteed:
Commercial		2,031,532		—		233,055		1,798,477
Residential		9,979,882		—		1,306,934		8,672,948
Privately issued		44,319		9,041		7,374		45,986
Other debt securities		1,612		—		—		1,612
		15,571,120		9,041		1,815,218		13,764,943
Total debt securities	$	26,610,086	$	9,195	$	2,261,929	$	24,357,352
Equity and other securities:
Readily marketable equity — at fair value	$	260,688	$	2,425	$	3,897	$	259,216
Other — at cost		913,358		—		—		913,358
Total equity and other securities	$	1,174,046	$	2,425	$	3,897	$	1,172,574
December 31, 2022
Investment securities available for sale:
U.S. Treasury and federal agencies	$	7,913,932	$	200	$	243,172	$	7,670,960
Mortgage-backed securities:
Government issued or guaranteed:
Commercial		594,779		—		20,480		574,299
Residential		2,501,334		65		171,281		2,330,118
Other debt securities		183,107		250		9,773		173,584
		11,193,152		515		444,706		10,748,961
Investment securities held to maturity:
U.S. Treasury and federal agencies		1,054,035		—		45,747		1,008,288
Obligations of states and political subdivisions		2,577,078		4		116,512		2,460,570
Mortgage-backed securities:
Government issued or guaranteed:
Commercial		912,431		—		103,528		808,903
Residential		8,934,918		1,451		891,063		8,045,306
Privately issued		49,742		8,833		7,987		50,588
Other debt securities		1,765		—		—		1,765
		13,529,969		10,288		1,164,837		12,375,420
Total debt securities	$	24,723,121	$	10,803	$	1,609,543	$	23,124,381
Equity and other securities:
Readily marketable equity — at fair value	$	153,283	$	2,120	$	3,945	$	151,458
Other — at cost		780,483		—		—		780,483
Total equity and other securities	$	933,766	$	2,120	$	3,945	$	931,941

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

At September 30, 2023, the amortized cost and estimated fair value of debt securities by contractual maturity were as follows:

	Amortized Cost		Estimated Fair Value
	(In thousands)
Debt securities available for sale:
Due in one year or less	$	4,619,339	$	4,544,581
Due after one year through five years		3,437,580		3,306,540
Due after five years through ten years		24,974		22,400
Due after ten years		30,000		25,132
		8,111,893		7,898,653
Mortgage-backed securities available for sale		2,927,073		2,693,756
	$	11,038,966	$	10,592,409
Debt securities held to maturity:
Due in one year or less	$	14,164	$	13,967
Due after one year through five years		1,151,126		1,097,310
Due after five years through ten years		1,306,208		1,223,790
Due after ten years		1,043,889		912,465
		3,515,387		3,247,532
Mortgage-backed securities held to maturity		12,055,733		10,517,411
	$	15,571,120	$	13,764,943

Investment Securities in Continuous Unrealized Loss Position

A summary of investment securities that as of September 30, 2023 and December 31, 2022 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
	Fair Value		Unrealized Losses		Fair Value		Unrealized Losses
	(In thousands)
September 30, 2023
Investment securities available for sale:
U.S. Treasury and federal agencies	$	226,045	$	3,741	$	7,509,062	$	196,810
Mortgage-backed securities:
Government issued or guaranteed:
Commercial		81,949		5,146		443,520		13,648
Residential		240,610		13,246		1,926,504		201,285
Other debt securities		6,553		202		152,192		12,633
		555,157		22,335		10,031,278		424,376
Investment securities held to maturity:
U.S. Treasury and federal agencies		48,825		1,193		904,460		47,513
Obligations of states and political subdivisions		235,273		15,423		2,055,317		203,726
Mortgage-backed securities:
Government issued or guaranteed:
Commercial		1,015,480		97,998		782,997		135,057
Residential		2,570,788		146,021		6,102,160		1,160,913
Privately issued		1,927		82		32,081		7,292
		3,872,293		260,717		9,877,015		1,554,501
Total	$	4,427,450	$	283,052	$	19,908,293	$	1,978,877
December 31, 2022
Investment securities available for sale:
U.S. Treasury and federal agencies	$	6,706,413	$	183,760	$	841,945	$	59,412
Mortgage-backed securities:
Government issued or guaranteed:
Commercial		574,299		20,480		—		—
Residential		2,295,873		169,489		28,305		1,792
Other debt securities		93,458		3,604		73,280		6,169
		9,670,043		377,333		943,530		67,373
Investment securities held to maturity:
U.S. Treasury and federal agencies		1,008,288		45,747		—		—
Obligations of states and political subdivisions		2,449,420		116,512		—		—
Mortgage-backed securities:
Government issued or guaranteed:
Commercial		808,903		103,528		—		—
Residential		6,292,462		619,403		1,319,300		271,660
Privately issued		—		—		35,661		7,987
		10,559,073		885,190		1,354,961		279,647
Total	$	20,229,116	$	1,262,523	$	2,298,491	$	347,020