Debt Securities (Tables)

The amortized cost, gross unrealized gains and losses, and estimated fair value of debt securities held to maturity and debt securities available for sale are as follows:


	December 31, 2020
			Recognized in OCI (1)						Not recognized in OCI
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Carrying Value		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
	(In millions)
Debt securities held to maturity:


Mortgage-backed securities:
Residential agency	$	554	$	—	$	(19)	$	535	$	34	$	—	$	569
Commercial agency	589		—		(2)		587		59		—		646
	$	1,143	$	—	$	(21)	$	1,122	$	93	$	—	$	1,215

Debt securities available for sale:
U.S. Treasury securities	$	178	$	5	$	—	$	183					$	183
Federal agency securities	102		3		—		105						105

Mortgage-backed securities:
Residential agency	18,455		625		(4)		19,076						19,076
Residential non-agency	1		—		—		1						1
Commercial agency	5,659		346		(6)		5,999						5,999
Commercial non-agency	571		15		—		586						586
Corporate and other debt securities	1,126		78		—		1,204						1,204
	$	26,092	$	1,072	$	(10)	$	27,154					$	27,154


	December 31, 2019
			Recognized in OCI (1)						Not recognized in OCI
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Carrying Value		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
	(In millions)
Debt securities held to maturity:


Mortgage-backed securities:
Residential agency	$	736	$	—	$	(26)	$	710	$	22	$	—	$	732
Commercial agency	625		—		(3)		622		20		(2)		640
	$	1,361	$	—	$	(29)	$	1,332	$	42	$	(2)	$	1,372

Debt securities available for sale:
U.S. Treasury securities	$	180	$	2	$	—	$	182					$	182
Federal agency securities	42		1		—		43						43

Mortgage-backed securities:
Residential agency	15,336		218		(38)		15,516						15,516
Residential non-agency	1		—		—		1						1
Commercial agency	4,720		77		(31)		4,766						4,766
Commercial non-agency	639		8		—		647						647
Corporate and other debt securities	1,414		38		(1)		1,451						1,451
	$	22,332	$	344	$	(70)	$	22,606					$	22,606

(1)The gross unrealized losses recognized in OCI on securities held to maturity resulted from a transfer of securities available for sale to held to maturity in the second quarter of 2013.

The amortized cost and estimated fair value of debt securities held to maturity and debt securities available for sale at December 31, 2020, by contractual maturity, are shown below. Expected maturities will differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties.


	Amortized Cost		Estimated Fair Value
	(In millions)
Debt securities held to maturity:
Mortgage-backed securities:
Residential agency	$	554	$	569
Commercial agency	589		646
	$	1,143	$	1,215
Debt securities available for sale:
Due in one year or less	$	200	$	202
Due after one year through five years	828		873
Due after five years through ten years	267		299
Due after ten years	111		118
Mortgage-backed securities:
Residential agency	18,455		19,076
Residential non-agency	1		1
Commercial agency	5,659		5,999
Commercial non-agency	571		586
	$	26,092	$	27,154

The following tables present gross unrealized losses and the related estimated fair value of debt securities held to maturity and debt securities available for sale at December 31, 2020 and 2019. For debt securities transferred to held to maturity from available for sale, the analysis in the tables below is comparing the securities' original amortized cost to its current estimated fair value. These securities are segregated between investments that have been in a continuous unrealized loss position for less than twelve months and for twelve months or more.


	December 31, 2020
	Less Than Twelve Months				Twelve Months or More				Total
	Estimated Fair Value		Gross Unrealized Losses		Estimated Fair Value		Gross Unrealized Losses		Estimated Fair Value		Gross Unrealized Losses
	(In millions)







Debt securities available for sale:


Mortgage-backed securities:
Residential agency	$	914	$	(4)	$	101	$	—	$	1,015	$	(4)

Commercial agency	819		(6)		—		—		819		(6)


	$	1,733	$	(10)	$	101	$	—	$	1,834	$	(10)

Gross realized gains and gross realized losses on sales of debt securities available for sale are shown in the table below. The cost of securities sold is based on the specific identification method. As part of the Company's normal process for evaluating impairment, management did identify a limited number of positions where impairment was believed to exist in certain periods, as shown in the table below.



	2020		2019		2018
	(In millions)
Gross realized gains	$	5	$	16	$	4
Gross realized losses	(1)		(43)		(1)
Impairment	—		(1)		(2)
Securities gains (losses), net	$	4	$	(28)	$	1