PREMISES, EQUIPMENT, AND SOFTWARE - Narrative (Details) $ in Millions	12 Months Ended
Dec. 31, 2015 USD ($) sale-leaseback	Dec. 31, 2014 USD ($) sale-leaseback	Dec. 31, 2013 USD ($) sale-leaseback
Capital Leases of Lessee [Abstract]
Book value of capital leased assets	$ 47	$ 46
Capital leased assets accumulated depreciation	25	22
Depreciation expense	$ 116	$ 117	$ 138
Sale Leaseback Transaction
Number of sale-leaseback transactions entered into during period \| sale-leaseback	2	0	1
Sale leaseback transaction term	10 years		10 years
Gain on sale leaseback transaction	$ 9		$ 15
Deferred gain on sale leaseback transaction	1		14
Capitalized Software
Capitalized software, gross	1,300	$ 1,100
Capitalized software, accumulated amortization	532	387
Amortization of software	$ 146	$ 145	$ 102

Sale-leaseback Transaction, Number

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- Definition

Amount before accumulated depreciation of leased physical assets used in the normal conduct of business to produce goods and services.

+ References

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- Definition

The total charge for the use of long-lived depreciable assets subject to a lease meeting the criteria for capitalization.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6455314&loc=d3e45014-112735

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-Publisher FASB
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For each balance sheet presented, the amount of accumulated amortization for capitalized computer software costs.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 985
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6501960&loc=d3e128462-111756

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For each income statement presented, the amount charged to expense for amortization of capitalized computer software costs.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Amount before accumulated amortization of capitalized costs for computer software, including but not limited to, acquired and internally developed computer software.

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- Definition

The amount of expense recognized in the current period that reflects the allocation of the cost of tangible assets over the assets' useful lives. Includes production and non-production related depreciation.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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- Definition

Term of the lessee's leasing arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

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- Definition

The amount of the gain recorded in connection with the transaction involving the sale of property to another party and the lease of the property back to the seller to be recognized in future periods.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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The portion of the gain that will be recorded as income or a reduction in rent expense in future periods less amounts recognized in the current period.

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-Name Accounting Standards Codification
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