Loans and Related Allowance for Credit Losses, Commitments to Lend (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, temporary advance arrangements	$ 72,700.0
Total unfunded credit commitments	563,249.0	$ 585,064.0
Total Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total unfunded credit commitments	340,731.0	372,926.0
Commercial and industrial loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total unfunded credit commitments	314,135.0	346,991.0
Commercial real estate mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total unfunded credit commitments	9,360.0	8,206.0
Commercial real estate construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total unfunded credit commitments	17,236.0	17,729.0
Total Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total unfunded credit commitments	222,518.0	212,138.0
Real estate 1-4 family first mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total unfunded credit commitments	42,691.0	34,391.0
Real estate 1-4 family junior lien mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total unfunded credit commitments	36,301.0	36,916.0
Credit card [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total unfunded credit commitments	118,339.0	114,933.0
Other revolving credit and installment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total unfunded credit commitments	25,187.0	25,898.0
International [Member] | Total Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial letters of credit international	$ 981.3	$ 862.0