FAIR VALUE MEASUREMENT - Valuation Techniques and Inputs for Level 3 Nonrecurring Fair Value Measurements (Details)	12 Months Ended
Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Nonrecurring fair value changes included in earnings
Nonrecurring fair value measurements included in earnings	$ 42,000,000	$ 157,000,000
Loans held-for-sale
Nonrecurring fair value changes included in earnings
Nonrecurring fair value measurements included in earnings	0	(13,000,000)
Other real estate owned
Nonrecurring fair value changes included in earnings
Nonrecurring fair value measurements included in earnings	(1,000,000)	(2,000,000)
Loans
Nonrecurring fair value changes included in earnings
Nonrecurring fair value measurements included in earnings	(56,000,000)	(22,000,000)
Non-marketable equity securities
Nonrecurring fair value changes included in earnings
Nonrecurring fair value measurements included in earnings	99,000,000	194,000,000
Nonrecurring \| Level 3
Valuation techniques and inputs
Loans held-for-sale	1,330,000,000	1,794,000,000
Nonrecurring \| Level 3 \| Price-based
Valuation techniques and inputs
Loans held-for-sale	1,320,000,000	1,729,000,000
Other real estate owned	11,000,000	15,000,000
Alternative investment funds, fair value		66,000,000
Nonrecurring \| Level 3 \| Discounted Cash Flow
Valuation techniques and inputs
Loans	54,000,000
Nonrecurring \| Level 3 \| Recovery Analysis
Valuation techniques and inputs
Other real estate owned	5,000,000	2,000,000
Loans	100,000,000	251,000,000
Price \| Nonrecurring \| Level 3 \| Price-based \| Minimum
Valuation techniques and inputs
Loans held-for-sale, measurement input, value	86	81
Alternative investment measurement, value		46
Price \| Nonrecurring \| Level 3 \| Price-based \| Maximum
Valuation techniques and inputs
Loans held-for-sale, measurement input, value	100	100
Alternative investment measurement, value		1,514
Price \| Nonrecurring \| Level 3 \| Price-based \| Weighted Average
Valuation techniques and inputs
Loans held-for-sale, measurement input, value	99	98
Alternative investment measurement, value		570
Price \| Nonrecurring \| Level 3 \| Recovery Analysis \| Minimum
Valuation techniques and inputs
Other real estate owned, measurement input, value		56
Loans, measurement input, value		3
Price \| Nonrecurring \| Level 3 \| Recovery Analysis \| Maximum
Valuation techniques and inputs
Other real estate owned, measurement input, value		83
Loans, measurement input, value		85
Price \| Nonrecurring \| Level 3 \| Recovery Analysis \| Weighted Average
Valuation techniques and inputs
Other real estate owned, measurement input, value		58
Loans, measurement input, value		28
Price \| Nonrecurring \| Level 3 \| Loans \| Discounted Cash Flow \| Minimum
Valuation techniques and inputs
Loans, measurement input, value	2
Price \| Nonrecurring \| Level 3 \| Loans \| Discounted Cash Flow \| Maximum
Valuation techniques and inputs
Loans, measurement input, value	54
Price \| Nonrecurring \| Level 3 \| Loans \| Discounted Cash Flow \| Weighted Average
Valuation techniques and inputs
Loans, measurement input, value	$ 27
Appraised value \| Nonrecurring \| Level 3 \| Minimum
Valuation techniques and inputs
Loans, measurement input	17,521,218
Appraised value \| Nonrecurring \| Level 3 \| Maximum
Valuation techniques and inputs
Loans, measurement input	43,646,426
Appraised value \| Nonrecurring \| Level 3 \| Weighted Average
Valuation techniques and inputs
Loans, measurement input	30,583,822
Appraised value \| Nonrecurring \| Level 3 \| Price-based
Valuation techniques and inputs
Loans	$ 29,000,000
Appraised value \| Nonrecurring \| Level 3 \| Price-based \| Minimum
Valuation techniques and inputs
Other real estate owned, measurement input, value	2,297,358	8,394,102
Appraised value \| Nonrecurring \| Level 3 \| Price-based \| Maximum
Valuation techniques and inputs
Other real estate owned, measurement input, value	8,394,102	8,394,102
Appraised value \| Nonrecurring \| Level 3 \| Price-based \| Weighted Average
Valuation techniques and inputs
Other real estate owned, measurement input, value	$ 5,615,884	$ 8,394,102
Discount To Price \| Nonrecurring \| Level 3 \| Recovery Analysis \| Minimum
Valuation techniques and inputs
Other real estate owned, measurement input		0.1300
Discount To Price \| Nonrecurring \| Level 3 \| Recovery Analysis \| Maximum
Valuation techniques and inputs
Other real estate owned, measurement input		0.1300
Discount To Price \| Nonrecurring \| Level 3 \| Recovery Analysis \| Weighted Average
Valuation techniques and inputs
Other real estate owned, measurement input		0.1300
Recovery rate \| Nonrecurring \| Level 3 \| Recovery Analysis \| Minimum
Valuation techniques and inputs
Loans, measurement input	0.0057	0.3060
Recovery rate \| Nonrecurring \| Level 3 \| Recovery Analysis \| Maximum
Valuation techniques and inputs
Loans, measurement input	1.0000	1.0000
Recovery rate \| Nonrecurring \| Level 3 \| Recovery Analysis \| Weighted Average
Valuation techniques and inputs
Loans, measurement input	0.6478	0.5051
Cost of Capital \| Nonrecurring \| Level 3 \| Price-based
Valuation techniques and inputs
Loans	$ 47,000,000
Cost of Capital \| Nonrecurring \| Level 3 \| Price-based \| Minimum
Valuation techniques and inputs
Loans, measurement input	0.0010
Cost of Capital \| Nonrecurring \| Level 3 \| Price-based \| Maximum
Valuation techniques and inputs
Loans, measurement input	1.0000
Cost of Capital \| Nonrecurring \| Level 3 \| Price-based \| Weighted Average
Valuation techniques and inputs
Loans, measurement input	0.5484

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Amount of gain (loss) recognized in the income statement for an asset measured on a nonrecurring basis using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

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Fair value of investment other than investment in equity security, investment in debt security and equity method investment. Includes, but is not limited to, investment in certain entities that calculate net asset value per share. Example includes, but is not limited to, investment in hedge fund, venture capital fund, private equity fund, and real estate partnership or fund.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 6A
-Subparagraph (a)
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
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Carrying amount of other real estate not separately disclosed, including, but not limited to, real estate investments, real estate loans that qualify as investments in real estate, and premises that are no longer used in operations may also be included in real estate owned. This does not include real estate assets taken in settlement of troubled loans through surrender or foreclosure.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.10(4))
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- Definition

Value of input used to measure real estate owned by financial institution by financial institution which is not directly related to its business.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
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