| **GOODWILL AND OTHER INTANGIBLES (Tables)**                             | 9 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 nine-month period endedSeptember 30, 2015:  Retail Banking Auto Finance & Business Banking(2) Real Estate and Commercial Banking Global Corporate Banking(1) SCUSA Total  (in thousands)Goodwill at December 31, 2014 $1,815,729 $71,522 $1,406,048 $131,130 $5,467,582 $8,892,011Disposals during the period — — — — — —Additions during the period — — — — — —Re-allocations during the period (265,553) 374,546 (108,993) — — —Goodwill at September 30, 2015 $1,550,176 $446,068 $1,297,055 $131,130 $5,467,582 $8,892,011(1) The Global Corporate Banking ("GCB") was formerly designated as the Global Corporate Banking & Market & Large Corporate Banking segment and was renamed during the third quarter of 2015.(2) The Auto Finance & Business Banking was formerly designated as the Auto Finance and Alliances segment and was renamed during the third quarter of 2015. |
| 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.  September 30, 2015 December 31, 2014 NetCarryingAmount AccumulatedAmortization NetCarryingAmount AccumulatedAmortization (in thousands)Intangibles subject to amortization:       Dealer networks$514,643 $(65,357) $544,054 $(35,946)Chrysler relationship113,750 (25,000) 125,000 (13,750)Core deposit intangibles1,830 (294,012) 7,779 (288,063)Other intangibles6,234 (23,675) 8,655 (21,253)Total intangibles subject to amortization636,457 (408,044) 685,488 (359,012)Intangibles not subject to amortization:       Trade name50,000 — 50,000 —Total Intangibles$686,457 $(408,044) $735,488 $(359,012)                                                                                                                                                                                                                                                                                                          |
| Schedule of Finite-Lived Intangible Assets, Future Amortization Expense | The estimated aggregate amortization expense related to intangibles 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)2015 $64,432 $49,031 $15,4012016 57,163 — 57,1632017 55,055 — 55,0552018 54,702 — 54,7022019 54,501 — 54,501Thereafter 399,635 — 399,635                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |

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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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