LOAN SERVICING - Sensitivity of Fair Value to Changes in key Assumptions (Details) - Mortgage Servicing Rights - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2022	Dec. 31, 2021
Assumption for Fair Value as of Balance Sheet Date of Assets or Liabilities that relate to Transferor's Continuing Involvement [Line Items]
Weighted average life (months)	89 months 28 days	76 months 17 days
Constant prepayment rate (annualized)	8.40%	11.20%
Discount rate	9.50%	9.50%
Sensitivity analysis of fair value, change in interest rates, plus 2.00%	$ 11	$ 15
Sensitivity analysis of fair value, change in interest rates, plus 1.00%	6	9
Sensitivity analysis of fair value, change in interest rates, plus 0.50%	4	5
Sensitivity analysis of fair value, change in interest rates, plus 0.25%	2	3
Sensitivity analysis of fair value, change in interest rates, minus 0.25%	(3)	(3)
Sensitivity analysis of fair value, change in interest rates, minus 0.50%	$ (6)	$ (7)