Annual report pursuant to Section 13 and 15(d)

FAIR VALUES OF ASSETS AND LIABILITIES - Recurring basis (Details)

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FAIR VALUES OF ASSETS AND LIABILITIES - Recurring basis (Details) - USD ($)
$ in Thousands
Dec. 31, 2016
Aug. 16, 2016
Dec. 31, 2015
Assets measured at fair value on a recurring basis      
Loans held for investment $ 82,319 $ 56,000 $ 34,637
Trading account securities 133,295   36,997
Available-for-sale and other securities 15,562,837   8,775,441
Consumer loans 82,319    
U.S. Treasury securities      
Assets measured at fair value on a recurring basis      
Available-for-sale and other securities 5,497   5,472
Federal agencies: Mortgage-backed      
Assets measured at fair value on a recurring basis      
Available-for-sale and other securities 10,673,342   4,521,688
Federal agencies: Other agencies      
Assets measured at fair value on a recurring basis      
Available-for-sale and other securities 73,542   115,913
Municipal securities      
Assets measured at fair value on a recurring basis      
Available-for-sale and other securities 3,250,057   2,456,396
Corporate debt      
Assets measured at fair value on a recurring basis      
Available-for-sale and other securities 198,683   466,477
Recurring      
Assets measured at fair value on a recurring basis      
Mortgage loans held for sale 438,224   337,577
Trading account securities 133,295   36,997
Available-for-sale and other securities 15,015,133   8,442,655
MSRs 13,747   17,585
Derivative assets netting (181,940)   (161,297)
Derivative assets 238,219   274,872
Liabilities measured at fair value on a recurring basis      
Derivative liabilities netting (272,361)   (144,309)
Derivative liabilities 98,286   144,350
Short-term borrowings 474   1,770
Recurring | U.S. Treasury securities      
Assets measured at fair value on a recurring basis      
Available-for-sale and other securities 5,497   5,472
Recurring | Federal agencies: Mortgage-backed      
Assets measured at fair value on a recurring basis      
Available-for-sale and other securities 10,673,342   4,521,688
Recurring | Federal agencies: Other agencies      
Assets measured at fair value on a recurring basis      
Available-for-sale and other securities 73,542   115,913
Recurring | Municipal securities      
Assets measured at fair value on a recurring basis      
Trading account securities 1,148   4,159
Available-for-sale and other securities 3,250,057   2,456,396
Recurring | Asset-backed securities      
Assets measured at fair value on a recurring basis      
Available-for-sale and other securities 793,481   861,413
Recurring | Corporate debt      
Assets measured at fair value on a recurring basis      
Available-for-sale and other securities 198,683   466,477
Recurring | Other securities      
Assets measured at fair value on a recurring basis      
Trading account securities 132,147   32,838
Available-for-sale and other securities 20,531   15,296
Recurring | Level 1      
Assets measured at fair value on a recurring basis      
Mortgage loans held for sale 0   0
Loans held for investment 0   0
Trading account securities 132,147   32,475
Available-for-sale and other securities 22,085   16,869
MSRs 0   0
Derivative assets gross 0   0
Liabilities measured at fair value on a recurring basis      
Gross amounts of recognized liabilities 0   0
Short-term borrowings 474   0
Recurring | Level 1 | U.S. Treasury securities      
Assets measured at fair value on a recurring basis      
Available-for-sale and other securities 5,497   5,472
Recurring | Level 1 | Federal agencies: Mortgage-backed      
Assets measured at fair value on a recurring basis      
Available-for-sale and other securities 0   0
Recurring | Level 1 | Federal agencies: Other agencies      
Assets measured at fair value on a recurring basis      
Available-for-sale and other securities 0   0
Recurring | Level 1 | Municipal securities      
Assets measured at fair value on a recurring basis      
Trading account securities 0   0
Available-for-sale and other securities 0   0
Recurring | Level 1 | Asset-backed securities      
Assets measured at fair value on a recurring basis      
Available-for-sale and other securities 0   0
Recurring | Level 1 | Corporate debt      
Assets measured at fair value on a recurring basis      
Available-for-sale and other securities 0   0
Recurring | Level 1 | Other securities      
Assets measured at fair value on a recurring basis      
Trading account securities 132,147   32,475
Available-for-sale and other securities 16,588   11,397
Recurring | Level 2      
Assets measured at fair value on a recurring basis      
Mortgage loans held for sale 438,224   337,577
Loans held for investment 34,439   32,889
Trading account securities 1,148   4,522
Available-for-sale and other securities 12,119,001   6,229,898
MSRs 0   0
Derivative assets gross 414,412   429,448
Liabilities measured at fair value on a recurring basis      
Gross amounts of recognized liabilities 362,777   287,994
Short-term borrowings 0   1,770
Recurring | Level 2 | U.S. Treasury securities      
Assets measured at fair value on a recurring basis      
Available-for-sale and other securities 0   0
Recurring | Level 2 | Federal agencies: Mortgage-backed      
Assets measured at fair value on a recurring basis      
Available-for-sale and other securities 10,673,342   4,521,688
Recurring | Level 2 | Federal agencies: Other agencies      
Assets measured at fair value on a recurring basis      
Available-for-sale and other securities 73,542   115,913
Recurring | Level 2 | Municipal securities      
Assets measured at fair value on a recurring basis      
Trading account securities 1,148   4,159
Available-for-sale and other securities 452,013   360,845
Recurring | Level 2 | Asset-backed securities      
Assets measured at fair value on a recurring basis      
Available-for-sale and other securities 717,478   761,076
Recurring | Level 2 | Corporate debt      
Assets measured at fair value on a recurring basis      
Available-for-sale and other securities 198,683   466,477
Recurring | Level 2 | Other securities      
Assets measured at fair value on a recurring basis      
Trading account securities 0   363
Available-for-sale and other securities 3,943   3,899
Recurring | Level 3      
Assets measured at fair value on a recurring basis      
Mortgage loans held for sale 0   0
Loans held for investment 47,880    
Trading account securities 0   0
Available-for-sale and other securities 2,874,047   2,195,888
Consumer loans     1,748
MSRs 13,747   17,585
Derivative assets gross 5,747   6,721
Liabilities measured at fair value on a recurring basis      
Gross amounts of recognized liabilities 7,870   665
Short-term borrowings 0   0
Recurring | Level 3 | U.S. Treasury securities      
Assets measured at fair value on a recurring basis      
Available-for-sale and other securities 0   0
Recurring | Level 3 | Federal agencies: Mortgage-backed      
Assets measured at fair value on a recurring basis      
Available-for-sale and other securities 0   0
Recurring | Level 3 | Federal agencies: Other agencies      
Assets measured at fair value on a recurring basis      
Available-for-sale and other securities 0   0
Recurring | Level 3 | Municipal securities      
Assets measured at fair value on a recurring basis      
Trading account securities 0   0
Available-for-sale and other securities 2,798,044   2,095,551
Recurring | Level 3 | Asset-backed securities      
Assets measured at fair value on a recurring basis      
Available-for-sale and other securities 76,003   100,337
Recurring | Level 3 | Corporate debt      
Assets measured at fair value on a recurring basis      
Available-for-sale and other securities 0   0
Recurring | Level 3 | Other securities      
Assets measured at fair value on a recurring basis      
Trading account securities 0   0
Available-for-sale and other securities $ 0   $ 0