DERIVATIVE INSTRUMENTS - Summary of Characteristics of Interest Rate Swaps (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Interest Rate Swaps
Derivative [Line Items]
Current notional	$ 74,146,350,000	$ 70,465,700,000
Weighted average pay rate	1.84%	2.17%
Weighted average receive rate	1.89%	2.68%
Weighted average underlying years to maturity	4 years 2 months 23 days	4 years 3 months 3 days
Derivative, nonmonetary notional amount, percentage	0.75
Interest Rate Swaps | 0 - 3 years
Derivative [Line Items]
Current notional	$ 38,942,400,000	$ 31,900,200,000
Weighted average pay rate	1.60%	1.84%
Weighted average receive rate	1.84%	2.73%
Weighted average underlying years to maturity	1 year 3 months 14 days	1 year 2 months 15 days
Derivative instruments, minimum maturity period	0 years	0 years
Derivative Instruments maximum maturity period	3 years	3 years
Interest Rate Swaps | 3 - 6 years
Derivative [Line Items]
Current notional	$ 16,097,450,000	$ 16,603,200,000
Weighted average pay rate	1.77%	2.29%
Weighted average receive rate	1.87%	2.70%
Weighted average underlying years to maturity	4 years 3 months 18 days	4 years 3 months 18 days
Derivative instruments, minimum maturity period	3 years	3 years
Derivative Instruments maximum maturity period	6 years	6 years
Interest Rate Swaps | 6 - 10 years
Derivative [Line Items]
Current notional	$ 16,176,500,000	$ 18,060,900,000
Weighted average pay rate	2.20%	2.57%
Weighted average receive rate	2.02%	2.56%
Weighted average underlying years to maturity	9 years	8 years 7 months 13 days
Derivative instruments, minimum maturity period	6 years	6 years
Derivative Instruments maximum maturity period	10 years	10 years
Interest Rate Swaps | Greater than 10 years
Derivative [Line Items]
Current notional	$ 2,930,000,000	$ 3,901,400,000
Weighted average pay rate	3.76%	3.63%
Weighted average receive rate	1.86%	2.59%
Weighted average underlying years to maturity	17 years 10 months 17 days	17 years 3 months 29 days
Derivative instruments, minimum maturity period	10 years	10 years
Forward Starting Pay Fixed Swaps
Derivative [Line Items]
Current notional		$ 0
Overnight Index Swap
Derivative [Line Items]
Derivative, nonmonetary notional amount, percentage	0.25