| **GOODWILL AND OTHER INTANGIBLES (Tables)**                             | 3 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
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| **Goodwill and Intangible Assets Disclosure [Abstract]**                |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |
| Schedule of Goodwill                                                    | The following table presents activity in the Company's goodwill by its reportable segments for the three-month period endedMarch 31, 2016:  Consumer and Business Banking (1) Auto Finance & Business Banking Commercial Real Estate(2)  Commercial Banking(2) Global Corporate Banking SC Total  (in thousands)Goodwill at December 31, 2015 $1,550,321 $445,923 $— $1,297,055 $131,130 $1,019,960 $4,444,389Disposals during the period — — —   — — —Additions during the period — — —   — — —Impairment during the period — — —   — — —Re-allocations during the period 329,983 (445,923) 870,411 (754,471) — — —Goodwill at March 31, 2016 $1,880,304 $— $870,411 $542,584 $131,130 $1,019,960 $4,444,389 (1)  Consumer and Business Banking was formerly designated as the Retail Banking segment and was renamed during the first quarter of 2016.(2)  Commercial Real Estate and Commercial Banking were formerly disclosed as the combined Real Estate and Commercial Banking segment. |
| Schedule of Finite-Lived and Indefinite-Lived Intangible Assets         | The following table details amounts related to the Company's finite-lived and indefinite-lived intangible assets for the dates indicated.  March 31, 2016 December 31, 2015 NetCarryingAmount AccumulatedAmortization NetCarryingAmount AccumulatedAmortization (in thousands)Intangibles subject to amortization:       Dealer networks$495,036 $(84,964) $504,839 $(75,161)Chrysler relationship106,250 (32,500) 110,000 (28,750)Core deposit intangibles152 (295,690) 763 (295,079)Other intangibles4,679 (25,230) 5,453 (24,455)Total intangibles subject to amortization606,117 (438,384) 621,055 (423,445)Intangibles not subject to amortization:       Trade name18,000 — 38,300 —Total Intangibles$624,117 $(438,384) $659,355 $(423,445)                                                                                                                                                                                                                                                                                                                                                                                                                                                     |
| Schedule of Finite-Lived Intangible Assets, Future Amortization Expense | The estimated aggregate amortization expense related to intangibles, excluding any impairment charges, for each of the five succeeding calendar years ending December 31 is:Year Calendar Year Amount Recorded To Date Remaining Amount To Record  (in thousands)2016 $57,162 $14,938 $42,2252017 55,055 — 55,0552018 54,702 — 54,7022019 54,501 — 54,5012020 54,441 — 54,441Thereafter 345,194 — 345,194                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |

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| - Definition
Schedule of Finite-Lived and Indefinite-Lived Intangible Assets [Table Text Block]
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| - Definition
Tabular disclosure of goodwill by reportable segment and in total which includes a rollforward schedule.
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Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13854-109267
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| - Definition
Tabular disclosure of the amount of amortization expense expected to be recorded in succeeding fiscal years for finite-lived intangible assets.
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Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=26713463&loc=d3e16323-109275
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