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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

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- 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 + Details
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- Definition Weighted average pay rate for interest rate swaps. + References No definition available. + Details
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- 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 No definition available. + Details
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