DERIVATIVE INSTRUMENTS - Summary of Characteristics of Interest Rate Swaps (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Interest Rate Swaps
Derivative [Line Items]
Current Notional	$ 34,329,650,000	$ 74,146,350,000
Weighted Average Pay Rate	0.92%	1.84%
Weighted Average Receive Rate	0.37%	1.89%
Weighted Average Years to Maturity	3 years 11 months 8 days	4 years 2 months 23 days
Interest Rate Swaps | LIBOR
Derivative [Line Items]
Nonmonetary notional amount, percentage	0.17	0.75
Interest Rate Swaps | Federal Funds Rate
Derivative [Line Items]
Nonmonetary notional amount, percentage	0.72
Interest Rate Swaps | Overnight Index Swap
Derivative [Line Items]
Nonmonetary notional amount, percentage	0.11	0.25
Interest Rate Swaps | 0 - 3 years
Derivative [Line Items]
Current Notional	$ 23,680,150,000	$ 38,942,400,000
Weighted Average Pay Rate	0.27%	1.60%
Weighted Average Receive Rate	0.11%	1.84%
Weighted Average Years to Maturity	1 year 11 months 15 days	1 year 3 months 14 days
Minimum Maturity Period	0 years	0 years
Maximum Maturity Period	3 years	3 years
Interest Rate Swaps | 3 - 6 years
Derivative [Line Items]
Current Notional	$ 3,600,000,000	$ 16,097,450,000
Weighted Average Pay Rate	0.18%	1.77%
Weighted Average Receive Rate	0.09%	1.87%
Weighted Average Years to Maturity	4 years 2 months 15 days	4 years 3 months 18 days
Minimum Maturity Period	3 years	3 years
Maximum Maturity Period	6 years	6 years
Interest Rate Swaps | 6 - 10 years
Derivative [Line Items]
Current Notional	$ 5,565,500,000	$ 16,176,500,000
Weighted Average Pay Rate	1.40%	2.20%
Weighted Average Receive Rate	0.62%	2.02%
Weighted Average Years to Maturity	7 years 9 months 3 days	9 years
Minimum Maturity Period	6 years	6 years
Maximum Maturity Period	10 years	10 years
Interest Rate Swaps | Greater than 10 years
Derivative [Line Items]
Current Notional	$ 1,484,000,000	$ 2,930,000,000
Weighted Average Pay Rate	3.06%	3.76%
Weighted Average Receive Rate	0.36%	1.86%
Weighted Average Years to Maturity	20 years 6 months 7 days	17 years 10 months 17 days
Minimum Maturity Period	10 years	10 years
Forward Starting Pay Fixed Swaps
Derivative [Line Items]
Current Notional	$ 0	$ 0