Loans - Consumer, Excluding Credit Card Loan Portfolio (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 928,887	$ 969,415	$ 947,651
Consumer, excluding credit card
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	331,809	373,637	$ 375,958
Consumer, excluding credit card | Residential mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	197,456	231,078
Consumer, excluding credit card | Residential mortgage | Residential real estate – PCI
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	21,290	24,034
Consumer, excluding credit card | Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	24,954	28,340
Consumer, excluding credit card | Home equity | Residential real estate – PCI
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	7,753	8,963
Consumer, excluding credit card | Auto
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	61,410	63,573
Consumer, excluding credit card | Consumer & Business Banking
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	26,699	26,612
Consumer, excluding credit card | Fixed Rate Residential Mortgage | Prime mortgage | Residential real estate – PCI
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	4,164	4,690
Consumer, excluding credit card | Fixed Rate Residential Mortgage | Subprime mortgage | Residential real estate – PCI
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	1,797	1,945
Consumer, excluding credit card | Option ARMs | Residential real estate – PCI
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 7,576	$ 8,436