Loans - Consumer, Excluding Credit Card Loans, Loan Modifications, Nature and Extent of Modifications (Details) - Consumer, excluding credit card - loan	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Impaired [Line Items]
Percentage, sum of items by type, may exceed	100.00%
Total residential real estate – excluding PCI | Trial Modification
Financing Receivable, Impaired [Line Items]
Number of loans modified	3,604	5,705	6,644
Total residential real estate – excluding PCI | Permanent Modification
Financing Receivable, Impaired [Line Items]
Number of loans modified	8,252	8,162	7,441
Total residential real estate – excluding PCI | Interest rate reduction
Financing Receivable, Impaired [Line Items]
Concession granted	60.00%	76.00%	68.00%
Total residential real estate – excluding PCI | Term or payment extension
Financing Receivable, Impaired [Line Items]
Concession granted	70.00%	86.00%	86.00%
Total residential real estate – excluding PCI | Principal and/or interest deferred
Financing Receivable, Impaired [Line Items]
Concession granted	12.00%	18.00%	24.00%
Total residential real estate – excluding PCI | Principal forgiveness
Financing Receivable, Impaired [Line Items]
Concession granted	14.00%	16.00%	16.00%
Total residential real estate – excluding PCI | Other
Financing Receivable, Impaired [Line Items]
Concession granted	32.00%	14.00%	5.00%
Residential mortgage | Trial Modification
Financing Receivable, Impaired [Line Items]
Number of loans modified	1,283	1,945	2,711
Residential mortgage | Permanent Modification
Financing Receivable, Impaired [Line Items]
Number of loans modified	2,628	3,338	3,145
Residential mortgage | Interest rate reduction
Financing Receivable, Impaired [Line Items]
Concession granted	63.00%	76.00%	71.00%
Residential mortgage | Term or payment extension
Financing Receivable, Impaired [Line Items]
Concession granted	72.00%	90.00%	81.00%
Residential mortgage | Principal and/or interest deferred
Financing Receivable, Impaired [Line Items]
Concession granted	15.00%	16.00%	27.00%
Residential mortgage | Principal forgiveness
Financing Receivable, Impaired [Line Items]
Concession granted	16.00%	26.00%	28.00%
Residential mortgage | Other
Financing Receivable, Impaired [Line Items]
Concession granted	33.00%	25.00%	11.00%
Home equity | Trial Modification
Financing Receivable, Impaired [Line Items]
Number of loans modified	2,321	3,760	3,933
Home equity | Permanent Modification
Financing Receivable, Impaired [Line Items]
Number of loans modified	5,624	4,824	4,296
Home equity | Interest rate reduction
Financing Receivable, Impaired [Line Items]
Concession granted	59.00%	75.00%	66.00%
Home equity | Term or payment extension
Financing Receivable, Impaired [Line Items]
Concession granted	69.00%	83.00%	89.00%
Home equity | Principal and/or interest deferred
Financing Receivable, Impaired [Line Items]
Concession granted	10.00%	19.00%	23.00%
Home equity | Principal forgiveness
Financing Receivable, Impaired [Line Items]
Concession granted	13.00%	9.00%	7.00%
Home equity | Other
Financing Receivable, Impaired [Line Items]
Concession granted	31.00%	6.00%	0.00%