Note Debt Securities Available for Sale (Amortized cost, gross unrealized gains and losses, approximate fair value, weighted average yield and contractual maturities of debt securities AFS) (Detail) - USD ($) $ in Thousands	Mar. 31, 2019		Dec. 31, 2018
Debt Securities, Available-for-sale
Debt securities available-for-sale, at fair value	$ 13,542,695		$ 13,300,184
Gross Unrealized Gains	59,078		30,929
Gross Unrealized Losses	127,744		209,307
Amortized Cost	13,611,361	[1]	13,478,562	[2]
Amortized cost
Amortized Cost	13,611,361		13,478,562
Gross unrealized gains
Gross unrealized gains	59,078		30,929
Gross unrealized loss
Gross unrealized losses	127,744		209,307
Fair Value
Fair Value	$ 13,542,695		$ 13,300,184
Weighted average yield
Weighted Average Yield	2.29%		2.25%
US Treasury Securities
Amortized cost
Amortized cost - Within 1 year	$ 3,453,820		$ 3,565,571
Amortized cost - After 1 to 5 years	4,559,672		4,483,741
Amortized cost - After 5 to 10 years	2,988		245,891
Amortized Cost	8,016,480		8,295,203
Gross unrealized gains
Gross unrealized gain - Within 1 year	677		108
Gross unrealized gain - After 1 to 5 years	34,676		13,647
Gross unrealized gain - After 5 to 10 years	138		3,770
Gross unrealized gains	35,491		17,525
Gross unrealized loss
Gross unrealized losses - Within 1 year	4,064		5,319
Gross unrealized losses - After 1 to 5 years	16,420		35,213
Gross unrealized losses - After 5 to 10 years	0		0
Gross unrealized losses	20,484		40,532
Fair Value
Fair value - Within 1 year	3,450,433		3,560,360
Fair value - After 1 to 5 years	4,577,928		4,462,175
Fair value - After 5 to 10 years	3,126		249,661
Fair Value	$ 8,031,487		$ 8,272,196
Weighted average yield
Weighted average yield - Within 1 year	2.06%		2.10%
Weighted average yield - After 1 to 5 years	2.31%		2.25%
Weighted average yield - After 5 to 10 years	3.06%		2.84%
Weighted Average Yield	2.20%		2.21%
Obligations of U.S. Government sponsored entities
Amortized cost
Amortized cost - Within 1 year	$ 181,084		$ 212,951
Amortized cost - After 1 to 5 years	85,737		123,857
Amortized Cost	266,821		336,808
Gross unrealized gains
Gross unrealized gain - Within 1 year	3		0
Gross unrealized gain - After 1 to 5 years	7		1
Gross unrealized gains	10		1
Gross unrealized loss
Gross unrealized losses - Within 1 year	980		1,406
Gross unrealized losses - After 1 to 5 years	1,180		2,094
Gross unrealized losses	2,160		3,500
Fair Value
Fair value - Within 1 year	180,107		211,545
Fair value - After 1 to 5 years	84,564		121,764
Fair Value	$ 264,671		$ 333,309
Weighted average yield
Weighted average yield - Within 1 year	1.45%		1.44%
Weighted average yield - After 1 to 5 years	1.49%		1.51%
Weighted Average Yield	1.46%		1.47%
Obligations of Puerto Rico, States and political subdivisions
Amortized cost
Amortized cost - Within 1 year	$ 6,975
Amortized cost - After 1 to 5 years			$ 6,926
Amortized Cost	6,975		6,926
Gross unrealized gains
Gross unrealized gain - Within 1 year	0
Gross unrealized gain - After 1 to 5 years			0
Gross unrealized gains	0		0
Gross unrealized loss
Gross unrealized losses - Within 1 year	166
Gross unrealized losses - After 1 to 5 years			184
Gross unrealized losses	166		184
Fair Value
Fair value - Within 1 year	6,809
Fair value - After 1 to 5 years			6,742
Fair Value	$ 6,809		$ 6,742
Weighted average yield
Weighted average yield - Within 1 year	0.00%
Weighted average yield - After 1 to 5 years			0.70%
Weighted Average Yield	0.00%		0.70%
Collateralized Mortgage Obligations - Federal agencies
Amortized cost
Amortized cost - After 1 to 5 years	$ 1,082		$ 749
Amortized cost - After 5 to 10 years	107,033		115,744
Amortized cost - After 10 years	612,396		638,995
Amortized Cost	720,511		755,488
Gross unrealized gains
Gross unrealized gain - After 1 to 5 years	0		0
Gross unrealized gain - After 5 to 10 years	0		1
Gross unrealized gain - After 10 years	2,260		1,584
Gross unrealized gains	2,260		1,585
Gross unrealized loss
Gross unrealized losses - After 1 to 5 years	8		7
Gross unrealized losses - After 5 to 10 years	3,502		4,715
Gross unrealized losses - After 10 years	17,495		23,680
Gross unrealized losses	21,005		28,402
Fair Value
Fair value - After 1 to 5 years	1,074		742
Fair value - After 5 to 10 years	103,531		111,030
Fair value - After 10 years	597,161		616,899
Fair Value	$ 701,766		$ 728,671
Weighted average yield
Weighted average yield - After 1 to 5 years	2.01%		1.92%
Weighted average yield - After 5 to 10 years	1.68%		1.71%
Weighted average yield - After 10 years	2.10%		2.10%
Weighted Average Yield	2.04%		2.04%
Mortgage Backed Securities
Amortized cost
Amortized cost - Within 1 year	$ 135		$ 431
Amortized cost - After 1 to 5 years	14,133		6,762
Amortized cost - After 5 to 10 years	347,822		365,727
Amortized cost - After 10 years	4,238,051		3,710,731
Amortized Cost	4,600,141		4,083,651
Gross unrealized gains
Gross unrealized gain - Within 1 year	1		4
Gross unrealized gain - After 1 to 5 years	206		43
Gross unrealized gain - After 5 to 10 years	1,156		1,090
Gross unrealized gain - After 10 years	19,949		10,679
Gross unrealized gains	21,312		11,816
Gross unrealized loss
Gross unrealized losses - Within 1 year	0		0
Gross unrealized losses - After 1 to 5 years	1		1
Gross unrealized losses - After 5 to 10 years	5,621		8,499
Gross unrealized losses - After 10 years	78,307		128,189
Gross unrealized losses	83,929		136,689
Fair Value
Fair value - Within 1 year	136		435
Fair value - After 1 to 5 years	14,338		6,804
Fair value - After 5 to 10 years	343,357		358,318
Fair value - After 10 years	4,179,693		3,593,221
Fair Value	$ 4,537,524		$ 3,958,778
Weighted average yield
Weighted average yield - Within 1 year	4.15%		4.30%
Weighted average yield - After 1 to 5 years	3.14%		2.74%
Weighted average yield - After 5 to 10 years	2.15%		2.19%
Weighted average yield - After 10 years	2.55%		2.45%
Weighted Average Yield	2.52%		2.43%
Other
Amortized cost
Amortized cost - After 5 to 10 years	$ 433		$ 486
Amortized Cost	433		486
Gross unrealized gains
Gross unrealized gain - After 5 to 10 years	5		2
Gross unrealized gains	5		2
Gross unrealized loss
Gross unrealized losses - After 5 to 10 years	0		0
Gross unrealized losses	0		0
Fair Value
Fair value - After 5 to 10 years	438		488
Fair Value	$ 438		$ 488
Weighted average yield
Weighted average yield - After 5 to 10 years	3.62%		3.62%
Weighted Average Yield	3.62%		3.62%

[1] Includes $10 billion pledged to secure public and trust deposits, assets sold under agreements to repurchase, credit facilities and loan servicing agreements that the secured parties are not permitted to sell or repledge the collateral, of which $8.9 billion serve as collateral for public funds.

[2] Includes $8.9 billion pledged to secure public and trust deposits, assets sold under agreements to repurchase, credit facilities and loan servicing agreements that the secured parties are not permitted to sell or repledge the collateral, of which $7.9 billion serve as collateral for public funds.