Summary of Significant Accounting Policies - Schedule of Loans and Leases Past Due Policies (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($)
Loans and Leases Receivable Disclosure [Line Items]
Sustained performance period to return to accrual status	180 days
Threshold period for past due classification of loans and leases receivable	30 days
Collateral on impaired loans and foreclosed properties, valuation period	6 months
Commercial
Loans and Leases Receivable Disclosure [Line Items]
Threshold amount for annual risk ratings review (or more)	$ 2
Threshold amount to be subjected to automated loan review system that produces a score for evaluating reserves (less than)	2
Threshold amount to establish a reserve on nonaccrual loans (or more)	3
Commercial | Minimum
Loans and Leases Receivable Disclosure [Line Items]
Threshold amount to establish a reserve on collateral dependent loans based upon the underlying collateral value, net of costs to sell	1
Commercial | Maximum
Loans and Leases Receivable Disclosure [Line Items]
Threshold amount to establish a reserve on collateral dependent loans based upon the underlying collateral value, net of costs to sell	$ 3
Commercial | Commercial and industrial
Loans and Leases Receivable Disclosure [Line Items]
Threshold period for nonaccrual status classification of loans	90 days	[1],[2]
Threshold period past due for charge down of loans	90 days
Commercial | CRE
Loans and Leases Receivable Disclosure [Line Items]
Threshold period for nonaccrual status classification of loans	90 days	[1],[2]
Threshold period past due for charge down of loans	90 days
Commercial | Lease financing
Loans and Leases Receivable Disclosure [Line Items]
Threshold period for nonaccrual status classification of loans	90 days	[1],[2]
Threshold period past due for charge down of loans	90 days
Retail | Residential mortgage | Minimum
Loans and Leases Receivable Disclosure [Line Items]
Threshold period for nonaccrual status classification of loans	90 days	[1],[3]
Threshold period past due for charge down of loans	90 days	[3]
Retail | Residential mortgage | Maximum
Loans and Leases Receivable Disclosure [Line Items]
Threshold period for nonaccrual status classification of loans	180 days	[1],[3]
Threshold period past due for charge down of loans	210 days	[3]
Retail | Direct | Minimum
Loans and Leases Receivable Disclosure [Line Items]
Threshold period for nonaccrual status classification of loans	90 days	[1],[3]
Threshold period past due for charge down of loans	90 days	[3]
Retail | Direct | Maximum
Loans and Leases Receivable Disclosure [Line Items]
Threshold period for nonaccrual status classification of loans	120 days	[1],[3]
Threshold period past due for charge down of loans	120 days	[3]
Retail | Indirect | Minimum
Loans and Leases Receivable Disclosure [Line Items]
Threshold period for nonaccrual status classification of loans	90 days	[1],[3]
Threshold period past due for charge down of loans	90 days	[3]
Retail | Indirect | Maximum
Loans and Leases Receivable Disclosure [Line Items]
Threshold period for nonaccrual status classification of loans	120 days	[1],[3]
Threshold period past due for charge down of loans	120 days	[3]
Revolving credit | Minimum
Loans and Leases Receivable Disclosure [Line Items]
Threshold period past due for charge down of loans	90 days	[3]
Revolving credit | Maximum
Loans and Leases Receivable Disclosure [Line Items]
Threshold period past due for charge down of loans	180 days	[3]

[1] Loans may be returned to accrual status when they become current as to both principal and interest and concern no longer exists as to the collectability of principal and interest, generally indicated by 180 days of sustained performance.

[2] Or when it is probable that principal or interest is not fully collectible, whichever occurs first.

[3] Depends on product type, loss mitigation status and status of the government guaranty.