Huntington Bancshares Incorporated Quarterly report pursuant to Section 13 or 15(d)

LOANS / LEASES AND ALLOWANCE FOR CREDIT LOSSES LOANS / LEASES AND ALLOWANCE FOR CREDIT LOSSES - Certain Loans Acquired Ending and Unpaid Balances (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Purchased Credit Impaired, Ending Balance	$ 64,989		$ 102,380
Loans and Leases Receivable, Allowance	675,486	$ 667,996	638,413	$ 616,898	$ 623,064	$ 597,843
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Allowance	474,122	$ 474,576	451,091	$ 431,795	$ 424,507	$ 398,753
Commercial \| Commercial and Industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Purchased Credit Impaired, Ending Balance	48,606		68,338
FirstMerit Corporation
Accounts, Notes, Loans and Financing Receivable [Line Items]
Purchased Credit Impaired, Ending Balance	64,989		102,380
Purchased Credit Impaired, Unpaid Balance	101,806		156,351
FirstMerit Corporation \| Commercial \| Commercial and Industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Purchased Credit Impaired, Ending Balance	48,606		68,338
Purchased Credit Impaired, Unpaid Balance	72,117		100,031
FirstMerit Corporation \| Commercial \| Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Purchased Credit Impaired, Ending Balance	16,383		34,042
Purchased Credit Impaired, Unpaid Balance	$ 29,689		$ 56,320