Note Investment Securities Available for Sale (AFS securities in a continuous unrealized loss position) (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	$ 311,324	$ 2,962,984
Less than 12 months Gross Unrealized Losses	941	21,762
12 months or more Fair Value	771,867	1,037,791
12 months or more Gross Unrealized Losses	19,936	41,601
Total Fair Value	1,083,191	4,000,775
Total Gross Unrealized Losses	20,877	63,363
US Treasury Securities
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value		589,689
Less than 12 months Gross Unrealized Losses		1,999
12 months or more Fair Value		0
12 months or more Gross Unrealized Losses		0
Total Fair Value		589,689
Total Gross Unrealized Losses		1,999
Obligations of U.S. Government sponsored entities
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	73,342	390,319
Less than 12 months Gross Unrealized Losses	113	2,128
12 months or more Fair Value	19,376	181,744
12 months or more Gross Unrealized Losses	54	2,680
Total Fair Value	92,718	572,063
Total Gross Unrealized Losses	167	4,808
Obligations of Puerto Rico, States and political subdivisions
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	6,229	884
Less than 12 months Gross Unrealized Losses	10	164
12 months or more Fair Value	15,515	19,490
12 months or more Gross Unrealized Losses	8,083	9,214
Total Fair Value	21,744	20,374
Total Gross Unrealized Losses	8,093	9,378
Collateralized Mortgage Obligations - Federal agencies
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	0	331,501
Less than 12 months Gross Unrealized Losses	0	4,446
12 months or more Fair Value	656,971	814,195
12 months or more Gross Unrealized Losses	11,325	28,874
Total Fair Value	656,971	1,145,696
Total Gross Unrealized Losses	11,325	33,320
Mortgage Backed Securities
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	231,705	1,641,663
Less than 12 months Gross Unrealized Losses	816	12,992
12 months or more Fair Value	80,005	22,362
12 months or more Gross Unrealized Losses	474	833
Total Fair Value	311,710	1,664,025
Total Gross Unrealized Losses	1,290	13,825
Equity securities
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	48	45
Less than 12 months Gross Unrealized Losses	2	5
12 months or more Fair Value	0	0
12 months or more Gross Unrealized Losses	0	0
Total Fair Value	48	45
Total Gross Unrealized Losses	$ 2	5
Other
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value		8,883
Less than 12 months Gross Unrealized Losses		28
12 months or more Fair Value		0
12 months or more Gross Unrealized Losses		0
Total Fair Value		8,883
Total Gross Unrealized Losses		$ 28