| **INVESTMENT SECURITIES (Tables)**                                    | 9 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
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| **Investments, Debt and Equity Securities [Abstract]**                |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |
| Summary of Available-for-sale Securities                              | The following tables present the amortized cost, gross unrealized gains and losses and approximate fair values of securities available-for-sale at the dates indicated: September 30, 2015 AmortizedCost GrossUnrealizedGains GrossUnrealizedLoss FairValue (in thousands)U.S. Treasury securities$3,191,564 $18,299 $— $3,209,863Corporate debt securities1,554,216 17,224 (8,341) 1,563,099Asset-backed securities ("ABS")1,938,581 7,111 (1,041) 1,944,651Equity securities10,826 3 (301) 10,528State and municipal securities750,946 12,524 (2,148) 761,322Mortgage-backed securities:       U.S. government agencies - Residential4,077,361 31,836 (16,724) 4,092,473U.S. government agencies - Commercial986,989 10,283 (5,109) 992,163FHLMC and FNMA - Residential debt securities (1)8,379,831 46,998 (89,154) 8,337,675FHLMC and FNMA - Commercial debt securities138,383 1,402 (427) 139,358Non-agency securities52 — — 52Total investment securities available-for-sale$21,028,749 $145,680 $(123,245) $21,051,184(1) Federal Home Loan Mortgage Corporation ("FHLMC") and Federal National Mortgage Association ("FNMA") December 31, 2014 AmortizedCost GrossUnrealizedGains GrossUnrealizedLoss FairValue (in thousands)U.S. Treasury securities$1,692,838 $2,985 $(56) $1,695,767Corporate debt securities2,159,681 29,630 (6,910) 2,182,401Asset-backed securities2,707,207 17,787 (4,591) 2,720,403Equity securities10,619 3 (279) 10,343State and municipal securities1,790,776 35,071 (2,385) 1,823,462Mortgage-backed securities:       U.S. government agencies - Residential2,151,111 1,626 (33,811) 2,118,926U.S government agencies - Commercial472,611 183 (7,186) 465,608FHLMC and FNMA - Residential debt securities4,971,045 12,817 (129,990) 4,853,872FHLMC and FNMA - Commercial debt securities23,929 157 (171) 23,915Non-agency securities12,842 539 — 13,381Total investment securities available-for-sale$15,992,659 $100,798 $(185,379) $15,908,078                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |
| Investments Classified by Contractual Maturity Date                   | Contractual maturities of the Company’s debt securities available-for-sale at September 30, 2015 are as follows: AmortizedCost FairValue (in thousands)Due within one year$676,336 $674,564Due after 1 year but within 5 years5,847,161 5,883,134Due after 5 years but within 10 years361,297 363,618Due after 10 years14,133,129 14,119,340Total$21,017,923 $21,040,656                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
| Gross Unrealized Loss and Fair Value of Securities Available-for-Sale | The following tables present the aggregate amount of unrealized losses as of September 30, 2015 and December 31, 2014 on securities in the Company’s available-for-sale investment portfolio classified according to the amount of time that those securities have been in a continuous loss position: September 30, 2015 Less than 12 months 12 months or longer Total Fair Value UnrealizedLosses Fair Value UnrealizedLosses Fair Value UnrealizedLosses (in thousands)Corporate debt securities$500,998 $(6,427) $136,932 $(1,914) $637,930 $(8,341)Asset-backed securities143,150 (1,041) — — 143,150 (1,041)Equity securities376 (2) 9,850 (299) 10,226 (301)State and municipal securities203,170 (1,217) 25,430 (931) 228,600 (2,148)Mortgage-backed securities:           U.S. government agencies - Residential400,513 (735) 972,042 (15,989) 1,372,555 (16,724)U.S government agencies - Commercial216,806 (2,551) 116,893 (2,558) 333,699 (5,109)FHLMC and FNMA - Residential1,219,050 (4,080) 2,245,972 (85,074) 3,465,022 (89,154)FHLMC and FNMA - Commercial42,195 (427) — — 42,195 (427)Total$2,726,258 $(16,480) $3,507,119 $(106,765) $6,233,377 $(123,245)NOTE 4. INVESTMENT SECURITIES (continued) December 31, 2014 Less than 12 months 12 months or longer Total Fair Value UnrealizedLosses Fair Value UnrealizedLosses Fair Value UnrealizedLosses (in thousands)US Treasury securities$298,914 $(56) $— $— $298,914 $(56)Corporate debt securities538,108 (3,262) 214,852 (3,648) 752,960 (6,910)Asset-backed securities632,936 (1,437) 424,333 (3,154) 1,057,269 (4,591)Equity securities55 — 9,879 (279) 9,934 (279)State and municipal securities45,128 (90) 192,091 (2,295) 237,219 (2,385)Mortgage-backed securities:           U.S. government agencies - Residential415,731 (2,693) 1,348,908 (31,118) 1,764,639 (33,811)U.S. government agencies - Commercial281,258 (2,459) 136,269 (4,727) 417,527 (7,186)FHLMC and FNMA - Residential debt securities399,176 (2,019) 2,607,695 (127,971) 3,006,871 (129,990)FHLMC and FNMA - Commercial debt securities11,269 (171) — — 11,269 (171)Total$2,622,575 $(12,187) $4,934,027 $(173,192) $7,556,602 $(185,379) |
| Gains (Losses) and Proceeds on Sales of Securities                    | Proceeds from sales of investment securities and the realized gross gains and losses from those sales are as follows: Three-Month PeriodEnded September 30,  Nine-Month PeriodEnded September 30, 2015 2014 2015 2014 (in thousands)Proceeds from the sales of available-for-sale securities$497,182 $21,138 $2,751,790 $311,019        Gross realized gains$533 $131 $23,592 $11,547Gross realized losses(2,526) — (5,229) (67)OTTI— — (1,092) —    Net realized (losses)/gains$(1,993) $131 $17,271 $11,480                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
| Gains (Losses) on Trading Securities                                  | The realized activity of trading gains and losses related to trading securities are as follows: Three-Month PeriodEnded September 30,  Nine-Month PeriodEnded September 30, 2015 2014 2015 2014 (in thousands)Net gains recognized during the period on trading securities$— $1,899 $6,391 $3,386Less: Net gains recognized during the period on trading securities sold during the period— 2,047 6,391 3,782Unrealized losses during the reporting period on trading securities still held at the reporting date$— $(148) $— $(396)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |

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Tabular disclosure of available-for-sale securities which includes, but is not limited to, changes in the cost basis and fair value, fair value and gross unrealized gain (loss), fair values by type of security, contractual maturity and classification, amortized cost basis, contracts to acquire securities to be accounted for as available-for-sale, debt maturities, transfers to trading, change in net unrealized holding gain (loss) net of tax, continuous unrealized loss position fair value, aggregate losses qualitative disclosures, other than temporary impairment (OTTI) losses or other disclosures related to available for sale securities.
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Tabular disclosure of investments in trading securities.
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