BUSINESS COMBINATIONS - Pro Forma (Details) - TCF Financial Corporation - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020
Business Acquisition [Line Items]
Net income attributable to Huntington Bancshares Inc	$ 1,624	$ 834
Net interest income
Business Acquisition [Line Items]
Pro forma revenue	4,713	4,774
Noninterest income
Business Acquisition [Line Items]
Pro forma revenue	$ 2,112	$ 2,127

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