VARIABLE INTEREST ENTITIES - Income Statement Effect (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Non-Interest Income
Amortization of tax credit investments under equity method, net of tax benefit	$ 0	$ 0	$ 1	$ 1
Provision for income taxes:
Amortization of LIHTC investments under proportional method	3	2	10	8
Low-income housing tax credits	(4)	(3)	(11)	(9)
Other tax benefits related to tax credit investments	0	0	(2)	(2)
Total impact on provision for income taxes	$ (1)	$ (1)	$ (3)	$ (3)