The following table summarizes the amortized cost and fair value of available-for-sale debt securities by major type:


	At March 31, 2022
(In thousands)	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value (1)
U.S. Treasury notes	$	754,313	$	—	$	(21,888)	$	732,425
Government agency debentures	227,161		84		(10,026)		217,219
Municipal bonds and notes	1,946,946		6		(52,415)		1,894,537
Agency CMO	80,766		127		(1,380)		79,513
Agency MBS	2,679,206		4,347		(108,984)		2,574,569
Agency CMBS	1,683,526		14		(99,720)		1,583,820
CMBS	871,981		265		(8,089)		864,157
CLO	14,245		—		(12)		14,233
Corporate debt	797,694		18		(30,668)		767,044
Other	17,500		—		(120)		17,380
Available-for-sale debt securities	$	9,073,338	$	4,861	$	(333,302)	$	8,744,897

	At December 31, 2021
(In thousands)	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value (1)
U.S. Treasury notes	$	398,664	$	—	$	(1,698)	$	396,966
Agency CMO	88,109		2,326		(51)		90,384
Agency MBS	1,568,293		36,130		(11,020)		1,593,403
Agency CMBS	1,248,548		2,537		(18,544)		1,232,541
CMBS	887,640		506		(1,883)		886,263
CLO	21,860		—		(13)		21,847
Corporate debt	14,583		—		(1,133)		13,450
Available-for-sale debt securities	$	4,227,697	$	41,499	$	(34,342)	$	4,234,854

The increase of $4.5 billion in available-for-sale debt securities from December 31, 2021 to March 31, 2022, is primarily attributed to $4.4 billion of investment securities acquired from Sterling in the merger, all of which were classified as available-for-sale based on Webster's intent at closing. Accrued interest receivable of $41.9 million and $7.5 million at March 31, 2022 and December 31, 2021, respectively, is excluded from amortized cost and is reported within accrued interest receivable and other assets on the accompanying Condensed Consolidated Balance Sheets.


	At March 31, 2022
	Less Than 12 Months				12 Months or More				Total
(Dollars in thousands)	Fair Value		Unrealized Losses		Fair Value		Unrealized Losses		# of Holdings	Fair Value		Unrealized Losses
U.S. Treasury notes	$	732,424	$	(21,888)	$	—	$	—	23	$	732,424	$	(21,888)
Government agency debentures	194,636		(10,026)		—		—		13	194,636		(10,026)
Municipal bonds and notes	1,887,526		(52,415)		—		—		533	1,887,526		(52,415)
Agency CMO	65,378		(1,380)		—		—		26	65,378		(1,380)
Agency MBS	2,097,135		(90,138)		171,877		(18,846)		392	2,269,012		(108,984)
Agency CMBS	1,234,865		(67,130)		348,893		(32,590)		132	1,583,758		(99,720)
CMBS	665,550		(7,265)		148,459		(824)		45	814,009		(8,089)
CLO	—		—		14,233		(12)		1	14,233		(12)
Corporate debt	753,284		(29,821)		9,460		(847)		104	762,744		(30,668)
Other	7,130		(120)		—		—		2	7,130		(120)
Available-for-sale debt securities in unrealized loss position	$	7,637,928	$	(280,183)	$	692,922	$	(53,119)	1,271	$	8,330,850	$	(333,302)


	At December 31, 2021
	Less Than Twelve Months				Twelve Months or Longer				Total
(Dollars in thousands)	Fair Value		Unrealized Losses		Fair Value		Unrealized Losses		# of Holdings	Fair Value		Unrealized Losses
U.S. Treasury notes	$	396,966	$	(1,698)	$	—	$	—	8	$	396,966	$	(1,698)
Agency CMO	7,895		(51)		—		—		2	7,895		(51)
Agency MBS	506,602		(7,354)		110,687		(3,666)		70	617,289		(11,020)
Agency CMBS	632,213		(6,163)		335,480		(12,381)		28	967,693		(18,544)
CMBS	724,762		(1,744)		81,253		(139)		50	806,015		(1,883)
CLO	—		—		21,848		(13)		1	21,848		(13)
Corporate debt	4,203		(76)		9,247		(1,057)		3	13,450		(1,133)
Available-for-sale debt securities in unrealized loss position	$	2,272,641	$	(17,086)	$	558,515	$	(17,256)	162	$	2,831,156	$	(34,342)

Webster assesses each available-for-sale debt security that is in an unrealized loss position to determine whether the decline in fair value below the amortized cost basis resulted from a credit loss or other factors. The increase in unrealized losses from December 31, 2021 to March 31, 2022 is primarily due to increased portfolio size from the merger with Sterling, and higher market rates. Market prices will approach par as the securities approach maturity.

At March 31, 2022, Webster had the intent to hold available-for-sale debt securities with unrealized losses through the anticipated recovery period, and it was more-likely-than-not that the Company would not have to sell these securities before recovery of their amortized cost basis. The issuers of these securities have not, to the Company’s knowledge, established any cause for default on these securities. As a result, the Company expects to recover the securities' entire amortized cost basis. Accordingly, no available-for-sale debt securities were in non-accrual status and there was no ACL recorded at both March 31, 2022 and December 31, 2021.

The following table summarizes the amortized cost and fair value of available-for-sale debt securities by contractual maturity:


	At March 31, 2022
(In thousands)	Amortized Cost		Fair Value
Due in one year or less	$	33,293	$	33,216
Due after one year through five years	1,346,552		1,311,044
Due after five through ten years	1,522,072		1,474,896
Due after ten years	6,171,421		5,925,741
Total available-for-sale debt securities	$	9,073,338	$	8,744,897

Available-for-sale debt securities that are not due at a single maturity date have been categorized based on the maturity date of the underlying collateral. Actual principal cash flows may differ from this categorization as borrowers have the right to repay their obligations with or without prepayment penalties.


(In thousands)	At March 31, 2022		At December 31, 2021
Available-for-sale debt securities pledged for deposits, at fair value	$	3,761,342	$	855,323
Available-for-sale debt securities pledged for borrowings and other, at fair value	902,581		924,841
Total available-for-sale debt securities pledged	$	4,663,923	$	1,780,164


	At March 31, 2022
(In thousands)	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value		Allowance		Net Carrying Value
Agency CMO	$	36,533	$	54	$	(856)	$	35,731	$	—	$	36,533
Agency MBS	2,915,114		8,452		(128,688)		2,794,878		—		2,915,114
Agency CMBS	2,548,347		33		(153,778)		2,394,602		—		2,548,347
Municipal bonds and notes	696,601		12,198		(4,138)		704,661		204		696,397
CMBS	165,863		62		(4,180)		161,745		—		165,863
Held-to-maturity debt securities	$	6,362,458	$	20,799	$	(291,640)	$	6,091,617	$	204	$	6,362,254


	At December 31, 2021
(In thousands)	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value		Allowance		Net Carrying Value
Agency CMO	$	42,405	$	655	$	(25)	$	43,035	$	—	$	42,405
Agency MBS	2,901,593		71,444		(11,788)		2,961,249		—		2,901,593
Agency CMBS	2,378,475		11,202		(43,844)		2,345,833		—		2,378,475
Municipal bonds and notes	705,918		51,572		—		757,490		214		705,704
CMBS	169,948		3,381		—		173,329		—		169,948
Held-to-maturity debt securities	$	6,198,339	$	138,254	$	(55,657)	$	6,280,936	$	214	$	6,198,125

Accrued interest receivable of $17.3 million and $21.2 million at March 31, 2022 and December 31, 2021, respectively, is excluded from amortized cost and is reported in accrued interest receivable and other assets on the accompanying Condensed Consolidated Balance Sheets.

An ACL on held-to-maturity debt securities is recorded for certain municipal bonds and notes to account for expected lifetime credit losses. Agency securities represent obligations issued by a U.S. government-sponsored enterprise or other federally-related entity and are either explicitly or implicitly guaranteed and therefore, assumed to be zero loss. Held-to-maturity debt securities with gross unrealized losses and no ACL are considered to be of high credit quality and therefore, zero credit loss is recorded as of March 31, 2022. The current period unrealized loss position of certain Agency CMBS is primarily attributed to the changing interest rate environment.

The following table summarizes the activity in the ACL on held-to-maturity debt securities:


	Three months ended March 31,
(In thousands)		2022		2021
Balance, beginning of period		$	214	$	299

(Benefit) provision for credit losses		(10)		9
Balance, end of period		$	204	$	308

The following table summarizes the amortized cost and fair value of held-to-maturity debt securities by contractual maturity:


	At March 31, 2022
(In thousands)	Amortized Cost		Fair Value
Due in one year or less	$	2,429	$	2,448
Due after one year through five years	52,963		54,861
Due after five years through ten years	309,859		306,139
Due after ten years	5,997,207		5,728,169
Total held-to-maturity debt securities	$	6,362,458	$	6,091,617

Held-to-maturity debt securities that are not due at a single maturity date have been categorized based on the maturity date of the underlying collateral. Actual principal cash flows may differ from this categorization as borrowers have the right to repay their obligations with or without prepayment penalties.

The Company monitors the credit quality of held-to-maturity debt securities through credit ratings provided by Standard & Poor's Rating Services (S&P), Moody's Investor Services (Moody's), Fitch Ratings, Inc., Kroll Bond Rating Agency, or DBRS Inc. Credit ratings express opinions about the credit quality of a debt security, and are updated at each quarter end. Investment grade debt securities are rated BBB- or higher by S&P, or Baa3 or higher by Moody's, and are generally considered by the rating agencies and market participants to be of low credit risk. Conversely, debt securities rated below investment grade, which are labeled as speculative grade by the rating agencies, are considered to have distinctively higher credit risk than investment grade debt securities. There were no speculative grade held-to-maturity debt securities at March 31, 2022 and December 31, 2021. Held-to-maturity debt securities that are not rated are collateralized with U.S. Treasury obligations.


	March 31, 2022
	Investment Grade
(In thousands)	Aaa		Aa1		Aa2		Aa3		A1		A2		A3		Baa2		Not Rated
Agency CMO	$	—	$	36,533	$	—	$	—	$	—	$	—	$	—	$	—	$	—
Agency MBS	—		2,915,114		—		—		—		—		—		—		—
Agency CMBS	—		2,548,347		—		—		—		—		—		—		—
Municipal bonds and notes	207,035		117,428		226,724		98,112		35,836		8,256		—		95		3,115
CMBS	165,863		—		—		—		—		—		—		—		—
Held-to-maturity debt securities	$	372,898	$	5,617,422	$	226,724	$	98,112	$	35,836	$	8,256	$	—	$	95	$	3,115


	December 31, 2021
	Investment Grade
(In thousands)	Aaa		Aa1		Aa2		Aa3		A1		A2		A3		Baa2		Not Rated
Agency CMO	$	—	$	42,405	$	—	$	—	$	—	$	—	$	—	$	—	$	—
Agency MBS	—		2,901,593		—		—		—		—		—		—		—
Agency CMBS	—		2,378,475		—		—		—		—		—		—		—
Municipal bonds and notes	207,426		119,804		227,106		104,232		35,878		8,260		—		95		3,117
CMBS	169,948		—		—		—		—		—		—		—		—
Held-to-maturity debt securities	$	377,374	$	5,442,277	$	227,106	$	104,232	$	35,878	$	8,260	$	—	$	95	$	3,117


(In thousands)	At March 31, 2022		At December 31, 2021
Held-to-maturity debt securities pledged for deposits, at amortized cost	$	1,858,753	$	1,834,117
Held-to-maturity debt securities pledged for borrowing and other, at amortized cost	1,026,796		1,243,139
Total held-to-maturity debt securities pledged	$	2,885,549	$	3,077,256