Quarterly report pursuant to Section 13 or 15(d)

AVAILABLE-FOR-SALE AND OTHER SECURITIES - Contractual Maturities (Details)

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AVAILABLE-FOR-SALE AND OTHER SECURITIES - Contractual Maturities (Details) - USD ($)
$ in Thousands
Sep. 30, 2016
Dec. 31, 2015
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis [Abstract]    
Amortized Cost $ 16,391,679 $ 8,770,923
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]    
Available-for-sale and other securities 16,470,374 8,775,441
U.S. Treasury    
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis [Abstract]    
Amortized Cost, Under 1 year 1,000 0
Amortized Cost, 1-5 years 5,474 5,457
Amortized Cost, 6-10 years 0 0
Amortized Cost, Over 10 years 0 0
Amortized Cost 6,474 5,457
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]    
Fair Value, Under 1 year 1,000 0
Fair Value, 1-5 years 5,509 5,472
Fair Value, 6-10 years 0 0
Fair Value, Over 10 years 0 0
Available-for-sale and other securities 6,509 5,472
Federal agencies: Mortgage-backed securities    
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis [Abstract]    
Amortized Cost, Under 1 year 0 51,146
Amortized Cost, 1-5 years 112,813 111,655
Amortized Cost, 6-10 years 268,553 254,397
Amortized Cost, Over 10 years 10,427,666 4,088,120
Amortized Cost 10,809,032 4,505,318
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]    
Fair Value, Under 1 year 0 51,050
Fair Value, 1-5 years 114,408 113,393
Fair Value, 6-10 years 274,530 257,765
Fair Value, Over 10 years 10,491,942 4,099,480
Available-for-sale and other securities 10,880,880 4,521,688
Federal agencies, Other agencies    
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis [Abstract]    
Amortized Cost, Under 1 year 1,851 801
Amortized Cost, 1-5 years 9,806 9,101
Amortized Cost, 6-10 years 111,561 105,174
Amortized Cost, Over 10 years 0 0
Amortized Cost 123,218 115,076
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]    
Fair Value, Under 1 year 1,878 805
Fair Value, 1-5 years 10,132 9,395
Fair Value, 6-10 years 113,761 105,713
Fair Value, Over 10 years 0 0
Available-for-sale and other securities 125,771 115,913
Total U.S. Treasury, Federal agency securities    
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis [Abstract]    
Amortized Cost 10,938,724 4,625,851
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]    
Available-for-sale and other securities 11,013,160 4,643,073
Municipal securities    
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis [Abstract]    
Amortized Cost, Under 1 year 171,499 281,644
Amortized Cost, 1-5 years 960,375 587,664
Amortized Cost, 6-10 years 1,434,758 1,053,502
Amortized Cost, Over 10 years 727,541 509,133
Amortized Cost 3,294,173 2,431,943
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]    
Fair Value, Under 1 year 165,902 280,823
Fair Value, 1-5 years 968,651 587,345
Fair Value, 6-10 years 1,440,241 1,048,550
Fair Value, Over 10 years 736,367 539,678
Available-for-sale and other securities 3,311,161 2,456,396
Asset-backed securities    
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis [Abstract]    
Amortized Cost, Under 1 year 0 0
Amortized Cost, 1-5 years 174,949 110,115
Amortized Cost, 6-10 years 292,649 128,342
Amortized Cost, Over 10 years 639,277 662,602
Amortized Cost 1,106,875 901,059
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]    
Fair Value, Under 1 year 0 0
Fair Value, 1-5 years 175,889 109,300
Fair Value, 6-10 years 295,441 128,208
Fair Value, Over 10 years 609,852 623,905
Available-for-sale and other securities 1,081,182 861,413
Corporate debt    
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis [Abstract]    
Amortized Cost, Under 1 year 79,248 300
Amortized Cost, 1-5 years 345,632 356,513
Amortized Cost, 6-10 years 66,223 107,394
Amortized Cost, Over 10 years 48,861 0
Amortized Cost 539,964 464,207
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]    
Fair Value, Under 1 year 80,146 302
Fair Value, 1-5 years 354,698 360,653
Fair Value, 6-10 years 68,428 105,522
Fair Value, Over 10 years 49,219 0
Available-for-sale and other securities 552,491 466,477
Other securities    
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis [Abstract]    
Amortized Cost, Under 1 year 0 0
Amortized Cost, 1-5 years 3,950 3,950
Amortized Cost, 6-10 years 0 0
Amortized Cost, Over 10 years 0 0
Amortized Cost 511,943 347,863
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]    
Fair Value, Under 1 year 0 0
Fair Value, 1-5 years 3,947 3,898
Fair Value, 6-10 years 0 0
Fair Value, Over 10 years 0 0
Available-for-sale and other securities 512,380 348,082
Non-marketable equity securities    
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis [Abstract]    
Amortized Cost 492,080 332,786
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]    
Available-for-sale and other securities 492,080 332,786
Mutual funds    
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis [Abstract]    
Amortized Cost 2,113 10,604
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]    
Available-for-sale and other securities 2,553 10,604
Marketable equity securities    
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis [Abstract]    
Amortized Cost 13,800 523
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]    
Available-for-sale and other securities $ 13,800 $ 794