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DERIVATIVE INSTRUMENTS - Summary of Characteristics of Interest Rate Swaps (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Interest rate swaps
Derivative [Line Items]
Current Notional	$ 67,458,400,000	$ 70,465,700,000
Weighted Average Pay Rate	2.20%	2.17%
Weighted Average Receive Rate	2.66%	2.68%
Weighted Average Underlying Years to Maturity	4 years 9 months 8 days	4 years 2 months 34 days
Interest rate swaps | 0 - 3 years
Derivative [Line Items]
Derivative Instruments minimum maturity period	0 years	0 years
Derivative Instruments maximum maturity period	3 years	3 years
Current Notional	$ 32,201,400,000	$ 31,900,200,000
Weighted Average Pay Rate	1.93%	1.84%
Weighted Average Receive Rate	2.66%	2.73%
Weighted Average Underlying Years to Maturity	1 year 4 months 46 days	1 year 2 months 16 days
Interest rate swaps | 3 - 6 years
Derivative [Line Items]
Derivative Instruments minimum maturity period	3 years	3 years
Derivative Instruments maximum maturity period	6 years	6 years
Current Notional	$ 13,567,000,000	$ 16,603,200,000
Weighted Average Pay Rate	2.12%	2.29%
Weighted Average Receive Rate	2.63%	2.70%
Weighted Average Underlying Years to Maturity	4 years 2 months 18 days	4 years 3 months 18 days
Interest rate swaps | 6 - 10 years
Derivative [Line Items]
Derivative Instruments minimum maturity period	6 years	6 years
Derivative Instruments maximum maturity period	10 years	10 years
Current Notional	$ 18,112,000,000	$ 18,060,900,000
Weighted Average Pay Rate	2.52%	2.57%
Weighted Average Receive Rate	2.70%	2.56%
Weighted Average Underlying Years to Maturity	8 years 11 months 10 days	8 years 7 months 12 days
Interest rate swaps | Greater than 10 years
Derivative [Line Items]
Derivative Instruments minimum maturity period	10 years	10 years
Current Notional	$ 3,578,000,000	$ 3,901,400,000
Weighted Average Pay Rate	3.59%	3.63%
Weighted Average Receive Rate	2.58%	2.59%
Weighted Average Underlying Years to Maturity	17 years 9 months 21 days	17 years 3 months 29 days
Forward Starting Pay Fixed Swaps
Derivative [Line Items]
Current Notional	$ 0	$ 0

X

- Definition

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

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- Definition

Derivative instruments maximum maturity period.

+ References

No definition available.

+ Details

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- Definition

Derivative instruments minimum maturity period.

+ References

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X

- Definition

Weighted average pay rate for interest rate swaps.

+ References

No definition available.

+ Details

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- Definition

Weighted average receive rate for interest rate swaps.

+ References

No definition available.

+ Details

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X

- Definition

Average remaining period until maturity of the derivative contract, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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