Loans - Repricing Characteristics (Details) $ in Millions	Dec. 31, 2017 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Due Over 1 But Within 5 Years	$ 25,876
Loans Due Over 5 Years	18,171
Receivables at predetermined interest rates [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Due Over 1 But Within 5 Years	1,535
Loans Due Over 5 Years	4,496
Receivables at floating or adjustable rates [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Due Over 1 But Within 5 Years	24,341
Loans Due Over 5 Years	$ 13,675