Loans - Consumer, Excluding Credit Card Loan Portfolio (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 940,440	$ 924,838	$ 899,576
Consumer, excluding credit card
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	374,587	372,553	$ 365,115
Consumer, excluding credit card | Residential mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	225,864	216,496
Consumer, excluding credit card | Residential mortgage | Residential real estate – PCI
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	26,977	30,576
Consumer, excluding credit card | Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	30,460	33,450
Consumer, excluding credit card | Home equity | Residential real estate – PCI
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	9,849	10,799
Consumer, excluding credit card | Auto
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	65,014	66,242
Consumer, excluding credit card | Consumer & Business Banking
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	26,272	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	5,437	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	2,249	2,609
Consumer, excluding credit card | Option ARMs | Residential real estate – PCI
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 9,442	$ 10,689