2. Investment securities

On January 1, 2018, the Company adopted amended guidance requiring equity investments with readily determinable fair values to be measured at fair value with changes in fair value recognized in the consolidated statement of income. This amended guidance excludes equity method investments, investments in consolidated subsidiaries, exchange membership ownership interests, and Federal Home Loan Bank of New York and Federal Reserve Bank of New York capital stock. Upon adoption the Company reclassified $17 million, after-tax effect, from accumulated other comprehensive income to retained earnings, representing the difference between fair value and the cost basis of equity investments with readily determinable fair values at January 1, 2018. Net unrealized losses recorded as gain (loss) on bank investment securities in the consolidated statement of income during the three months ended March 31, 2018 were $9 million. 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)
March 31, 2018
Investment securities available for sale:
U.S. Treasury and federal agencies	$	1,962,160		—		20,682	$	1,941,478
Obligations of states and political subdivisions		1,986		16		2		2,000
Mortgage-backed securities:
Government issued or guaranteed		8,407,476		21,318		206,665		8,222,129
Privately issued		27		—		—		27
Other debt securities		136,971		2,457		7,206		132,222
		10,508,620		23,791		234,555		10,297,856
Investment securities held to maturity:
Obligations of states and political subdivisions		20,209		75		36		20,248
Mortgage-backed securities:
Government issued or guaranteed		3,074,830		6,153		58,581		3,022,402
Privately issued		128,997		7,932		24,084		112,845
Other debt securities		4,720		—		—		4,720
		3,228,756		14,160		82,701		3,160,215
Total debt securities	$	13,737,376		37,951		317,256	$	13,458,071
Equity and other securities:
Readily marketable equity — at fair value		48,358		14,075		716		61,717
Other — at cost		478,235		—		—		478,235
Total equity and other securities	$	526,593		14,075		716	$	539,952

2. Investment securities, continued

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
	(In thousands)
December 31, 2017
Investment securities available for sale:
U.S. Treasury and federal agencies	$	1,965,665		—		18,178	$	1,947,487
Obligations of states and political subdivisions		2,555		36		2		2,589
Mortgage-backed securities:
Government issued or guaranteed		8,755,482		59,497		98,587		8,716,392
Privately issued		28		—		—		28
Other debt securities		136,905		2,402		10,475		128,832
Equity securities		78,161		23,219		424		100,956
		10,938,796		85,154		127,666		10,896,284
Investment securities held to maturity:
Obligations of states and political subdivisions		24,562		109		49		24,622
Mortgage-backed securities:
Government issued or guaranteed		3,187,953		27,236		13,746		3,201,443
Privately issued		135,688		2,574		27,575		110,687
Other debt securities		5,010		—		—		5,010
		3,353,213		29,919		41,370		3,341,762
Other securities — at cost		415,028		—		—		415,028
Total	$	14,707,037		115,073		169,036	$	14,653,074

There were no significant gross realized gains or losses from sales of investment securities for the quarters ended March 31, 2018 and 2017.

At March 31, 2018, 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	$	817,981		813,574
Due after one year through five years		1,151,292		1,134,986
Due after five years through ten years		82,301		82,049
Due after ten years		49,543		45,091
		2,101,117		2,075,700
Mortgage-backed securities available for sale		8,407,503		8,222,156
	$	10,508,620		10,297,856
Debt securities held to maturity:
Due in one year or less	$	11,410		11,432
Due after one year through five years		8,703		8,716
Due after five years through ten years		96		100
Due after ten years		4,720		4,720
		24,929		24,968
Mortgage-backed securities held to maturity		3,203,827		3,135,247
	$	3,228,756		3,160,215

2. Investment securities, continued

A summary of investment securities that as of March 31, 2018 and December 31, 2017 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)
March 31, 2018
Investment securities available for sale:
U.S. Treasury and federal agencies	$	241,594		(2,314	)		1,699,784		(18,368	)
Obligations of states and political subdivisions		1,020		(1	)		376		(1	)
Mortgage-backed securities:
Government issued or guaranteed		3,825,869		(68,681	)		3,023,992		(137,984	)
Other debt securities		4,341		(90	)		64,506		(7,116	)
		4,072,824		(71,086	)		4,788,658		(163,469	)

Investment securities held to maturity:
Obligations of states and political subdivisions		1,891		(4	)		5,454		(32	)
Mortgage-backed securities:
Government issued or guaranteed		2,280,618		(46,285	)		249,897		(12,296	)
Privately issued		—		—			53,852		(24,084	)
		2,282,509		(46,289	)		309,203		(36,412	)
Total	$	6,355,333		(117,375	)		5,097,861		(199,881	)

December 31, 2017
Investment securities available for sale:
U.S. Treasury and federal agencies	$	278,132		(1,761	)		1,669,355		(16,417	)
Obligations of states and political subdivisions		—		—			474		(2	)
Mortgage-backed securities:
Government issued or guaranteed		2,106,142		(13,695	)		3,138,841		(84,892	)
Other debt securities		3,067		(26	)		61,159		(10,449	)
Equity securities (a)		—		—			18,162		(424	)
		2,387,341		(15,482	)		4,887,991		(112,184	)

Investment securities held to maturity:
Obligations of states and political subdivisions		2,954		(4	)		6,110		(45	)
Mortgage-backed securities:
Government issued or guaranteed		1,331,759		(7,036	)		265,695		(6,710	)
Privately issued		5,061		(1,216	)		55,255		(26,359	)
		1,339,774		(8,256	)		327,060		(33,114	)
Total	$	3,727,115		(23,738	)		5,215,051		(145,298	)

(a)

Beginning January 1, 2018, equity securities with readily determinable fair values are required to be measured at fair value with changes in fair value recognized in the consolidated statement of income. As a result and as of March 31, 2018, disclosing the time period for which these equity securities had been in a continuous unrealized loss position is no longer relevant.

2. Investment securities, continued

The Company owned 1,442 individual debt securities with aggregate gross unrealized losses of $317 million at March 31, 2018. Based on a review of each of the securities in the investment securities portfolio at March 31, 2018, the Company concluded that it expected to recover the amortized cost basis of its investment. As of March 31, 2018, the Company does not intend to sell nor is it anticipated that it would be required to sell any of its impaired investment securities at a loss. At March 31, 2018, the Company has not identified events or changes in circumstances which may have a significant adverse effect on the fair value of the $478 million of cost method equity securities.