LOANS - Schedule of Interest Income Recognized for Non-Accrual Consumer Loans (Details) - Consumer - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Financing Receivable, Nonaccrual [Line Items]
Interest income	$ 5	$ 5
In North America offices
Financing Receivable, Nonaccrual [Line Items]
Interest income	5	5
In offices outside North America
Financing Receivable, Nonaccrual [Line Items]
Interest income	0	0
Residential first mortgages | In North America offices
Financing Receivable, Nonaccrual [Line Items]
Interest income	3	3
Residential first mortgages | In offices outside North America
Financing Receivable, Nonaccrual [Line Items]
Interest income	0	0
Home equity loans | In North America offices
Financing Receivable, Nonaccrual [Line Items]
Interest income	2	2
Credit cards | In North America offices
Financing Receivable, Nonaccrual [Line Items]
Interest income	0	0
Credit cards | In offices outside North America
Financing Receivable, Nonaccrual [Line Items]
Interest income	0	0
Personal, small business and other | In North America offices
Financing Receivable, Nonaccrual [Line Items]
Interest income	0	0
Personal, small business and other | In offices outside North America
Financing Receivable, Nonaccrual [Line Items]
Interest income	$ 0	$ 0