PREMISES, EQUIPMENT, AND SOFTWARE - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Capital Leases of Lessee [Abstract]
Depreciation expense	$ 117	$ 124	$ 130
Capitalized Software
Capitalized software, gross	1,800	1,700
Capitalized software, accumulated amortization	948	869
Amortization of software	189	180	$ 170
Assets subject to operating leases	$ 92	$ 112

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

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 985
-SubTopic 20
-Section 50
-Paragraph 1
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Amount of expense for amortization of capitalized computer software costs.

+ References

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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.

+ References

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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

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-Publisher FASB
-Name Accounting Standards Codification
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Amount before accumulated depreciation of physical assets used in the normal conduct of business to produce goods and services subject to or available for lease.

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