LOAN SALES AND SECURITIZATIONS - Residential Mortgage Portfolio, MSRs Fair Value Method (Details) - Home equity - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Servicing Asset at Fair Value, Amount [Roll Forward]
Fair value, beginning of year	$ 210	$ 7
Servicing assets obtained in acquisition	59	0
New servicing assets created	135	102
Time decay	(15)	(9)
Payoffs	(65)	(43)
Changes in valuation inputs or assumptions	27	(52)
Fair value, end of year	351	210
Revision of Prior Period, Adjustment
Servicing Asset at Fair Value, Amount [Roll Forward]
Fair value, beginning of year	$ 0	205
Fair value, end of year		$ 0
Sensitivity Analysis Fair Value Carrying Method
Servicing Asset at Fair Value, Amount [Roll Forward]
Weighted-average life (years)	7 years	7 years 7 months 6 days