Summary of Significant Accounting Policies and New Accounting Pronouncements - Charge-Off and Nonaccrual Policies and Practices (Details)	12 Months Ended
	Dec. 31, 2017
Credit Cards [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Notification period	60 days
Delinquent threshold period involving a bankruptcy	180 days
Commercial Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Number of days contractually delinquent	3 months
Consumer Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Number of days contractually delinquent	3 months
Period of consecutive payments	6 months
Delinquent threshold period	6 months
Update period	180 days
Valuation period from fair value determination date	90 days
Consumer Loans [Member] | Credit Cards [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Delinquent threshold period	6 months
Consumer Loans [Member] | Other consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Delinquent threshold period	4 months