LOANS - Corporate Loan Delinquency and Non-Accruals (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Loans receivable
Lease finance receivables	$ 675,883	$ 699,483
Loans at fair value	6,854	4,085
Leases
Loans receivable
Lease finance receivables	$ 700	1,400
Corporate
Loans receivable
Number of days past due, non-accrual status	90 days
Number of days past due for reversal of accrued interest and charging to earnings	90 days
Total loans past due and accruing	$ 2,144	2,380
Loans, total non-accrual	3,527	2,188
Loans, total current	374,533	381,300
Lease finance receivables	387,044	389,935
Loans at fair value	$ 6,840	4,067
Loans less than this number of days past due are considered current	30 days
Corporate | Commercial and industrial
Loans receivable
Total loans past due and accruing	$ 509	769
Loans, total non-accrual	2,795	1,828
Loans, total current	153,036	164,249
Lease finance receivables	156,340	166,846
Corporate | Financial institutions
Loans receivable
Total loans past due and accruing	733	794
Loans, total non-accrual	92	50
Loans, total current	86,864	91,008
Lease finance receivables	87,689	91,852
Corporate | Mortgage and real estate
Loans receivable
Total loans past due and accruing	697	538
Loans, total non-accrual	505	188
Loans, total current	70,836	62,425
Lease finance receivables	72,038	63,151
Corporate | Leases
Loans receivable
Total loans past due and accruing	74	67
Loans, total non-accrual	24	41
Loans, total current	640	1,277
Lease finance receivables	738	1,385
Corporate | Other
Loans receivable
Total loans past due and accruing	131	212
Loans, total non-accrual	111	81
Loans, total current	63,157	62,341
Lease finance receivables	63,399	62,634
30 to 89 Days Past Due | Corporate
Loans receivable
Total loans past due and accruing	1,692	2,249
30 to 89 Days Past Due | Corporate | Commercial and industrial
Loans receivable
Total loans past due and accruing	400	676
30 to 89 Days Past Due | Corporate | Financial institutions
Loans receivable
Total loans past due and accruing	668	791
30 to 89 Days Past Due | Corporate | Mortgage and real estate
Loans receivable
Total loans past due and accruing	450	534
30 to 89 Days Past Due | Corporate | Leases
Loans receivable
Total loans past due and accruing	62	58
30 to 89 Days Past Due | Corporate | Other
Loans receivable
Total loans past due and accruing	112	190
Equal to greater than 90 days past due | Corporate
Loans receivable
Total loans past due and accruing	452	131
Equal to greater than 90 days past due | Corporate | Commercial and industrial
Loans receivable
Total loans past due and accruing	109	93
Equal to greater than 90 days past due | Corporate | Financial institutions
Loans receivable
Total loans past due and accruing	65	3
Equal to greater than 90 days past due | Corporate | Mortgage and real estate
Loans receivable
Total loans past due and accruing	247	4
Equal to greater than 90 days past due | Corporate | Leases
Loans receivable
Total loans past due and accruing	12	9
Equal to greater than 90 days past due | Corporate | Other
Loans receivable
Total loans past due and accruing	$ 19	$ 22