BORROWED FUNDS - Short Term Borrowed Debt Key Data (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
Mar. 31, 2015	Dec. 31, 2014
Federal funds purchased and securities sold under agreements to repurchase
Short-term Debt [Line Items]
Weighted-average interest rate at period end	0.22%	0.14%
Maximum amount outstanding at month-end during the period	$ 5,375	$ 7,022
Average amount outstanding during the period	4,607	5,699
Weighted-average interest rate during the period	0.18%	0.12%
Other short-term borrowed funds (primarily current portion of FHLB advances)
Short-term Debt [Line Items]
Weighted-average interest rate at period end	0.26%	0.26%
Maximum amount outstanding at month-end during the period	7,004	7,702
Average amount outstanding during the period	$ 6,969	$ 5,640
Weighted-average interest rate during the period	0.26%	0.25%

The average effective interest rate during the reporting period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22(a)(1))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

For the form of debt having an initial term of less than one year or less than the normal operating cycle, if longer, average borrowings during the period.

+ References

No definition available.

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- Definition

For the form of debt having an initial term of less than one year or less than the normal operating cycle, if longer, maximum month-end borrowings during the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Industry Guide

-Number 3

-Section VII

-Subsection 2

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- Definition

Weighted average interest rate of short-term debt outstanding.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.19(b))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19

-Subparagraph b

-Article 5

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