Loans - Consumer, Excluding Credit Card Loan Portfolio (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 947,651	$ 924,838	$ 909,182
Consumer, excluding credit card
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	375,958	372,553	$ 369,413
Consumer, excluding credit card | Residential mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	231,361	216,496
Consumer, excluding credit card | Residential mortgage | Residential real estate – PCI
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	25,209	30,576
Consumer, excluding credit card | Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	29,318	33,450
Consumer, excluding credit card | Home equity | Residential real estate – PCI
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	9,393	10,799
Consumer, excluding credit card | Auto
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	63,619	66,242
Consumer, excluding credit card | Consumer & Business Banking
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	26,451	25,789
Consumer, excluding credit card | Fixed Rate Residential Mortgage | Prime mortgage | Residential real estate – PCI
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	4,931	6,479
Consumer, excluding credit card | Fixed Rate Residential Mortgage | Subprime mortgage | Residential real estate – PCI
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	2,072	2,609
Consumer, excluding credit card | Option ARMs | Residential real estate – PCI
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 8,813	$ 10,689