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 loss on bank investment securities in the consolidated statement of income during the three months and nine months ended September 30, 2018 were $3 million and $11 million, respectively. 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, 2018
Investment securities available for sale:
U.S. Treasury and federal agencies	$	1,623,860		8		15,196	$	1,608,672
Obligations of states and political subdivisions		1,792		9		5		1,796
Mortgage-backed securities:
Government issued or guaranteed		7,686,746		9,610		283,660		7,412,696
Privately issued		25		—		2		23
Other debt securities		137,552		1,911		8,135		131,328
		9,449,975		11,538		306,998		9,154,515
Investment securities held to maturity:
U.S. Treasury and federal agencies		445,199		—		412		444,787
Obligations of states and political subdivisions		8,752		32		18		8,766
Mortgage-backed securities:
Government issued or guaranteed		2,842,807		1,912		94,241		2,750,478
Privately issued		117,996		11,025		23,747		105,274
Other debt securities		3,965		—		—		3,965
		3,418,719		12,969		118,418		3,313,270
Total debt securities	$	12,868,694		24,507		425,416	$	12,467,785
Equity and other securities:
Readily marketable equity — at fair value	$	77,871		13,253		995	$	90,129
Other — at cost		410,518		—		—		410,518
Total equity and other securities	$	488,389		13,253		995	$	500,647

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 three-month and nine-month periods ended September 30, 2018 and 2017, respectively.

At September 30, 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	$	1,269,955		1,261,175
Due after one year through five years		361,249		354,788
Due after five years through ten years		101,971		101,055
Due after ten years		30,029		24,778
		1,763,204		1,741,796
Mortgage-backed securities available for sale		7,686,771		7,412,719
	$	9,449,975		9,154,515
Debt securities held to maturity:
Due in one year or less	$	448,774		448,366
Due after one year through five years		5,177		5,187
Due after ten years		3,965		3,965
		457,916		457,518
Mortgage-backed securities held to maturity		2,960,803		2,855,752
	$	3,418,719		3,313,270

2. Investment securities, continued

A summary of investment securities that as of September 30, 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)
September 30, 2018
Investment securities available for sale:
U.S. Treasury and federal agencies	$	9,221		(79	)		1,601,806		(15,117	)
Obligations of states and political subdivisions		702		(4	)		375		(1	)
Mortgage-backed securities:
Government issued or guaranteed		2,973,861		(80,037	)		3,628,562		(203,623	)
Privately issued		7		(2	)		—		—
Other debt securities		15,409		(127	)		63,639		(8,008	)
		2,999,200		(80,249	)		5,294,382		(226,749	)

Investment securities held to maturity:
U.S. Treasury and federal agencies		444,787		(412	)		—		—
Obligations of states and political subdivisions		514		(1	)		3,436		(17	)
Mortgage-backed securities:
Government issued or guaranteed		1,762,808		(52,208	)		800,906		(42,033	)
Privately issued		—		—			52,180		(23,747	)
		2,208,109		(52,621	)		856,522		(65,797	)
Total	$	5,207,309		(132,870	)		6,150,904		(292,546	)

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, subsequent to December 31, 2017 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 1,503 individual debt securities with aggregate gross unrealized losses of $425 million at September 30, 2018. Based on a review of each of the securities in the investment securities portfolio at September 30, 2018, the Company concluded that it expected to recover the amortized cost basis of its investment. As of September 30, 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 September 30, 2018, the Company has not identified events or changes in circumstances which may have a significant adverse effect on the fair value of the $411 million of cost method equity securities.