Loans - Credit Card Loan Portfolio (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Loans and Leases Receivable Disclosure [Line Items]
Retained	$ 969,415	$ 924,838	$ 889,907
Credit card
Loans and Leases Receivable Disclosure [Line Items]
Net charge-offs	$ 4,518	$ 4,123
% of net charge-offs to retained loans	3.10%	2.95%
Retained	$ 156,616	$ 149,387
% of 30 plus days past due to total retained loans	1.83%	1.80%
% of 90 plus days past due to total retained loans	0.92%	0.92%
Percentage of portfolio based on carrying value with estimated refreshed FICO scores, Equal to or greater than 660	84.20%	84.00%
Percentage of portfolio based on carrying value with estimated refreshed FICO scores, Less than 660	15.00%	14.60%
Percentage of portfolio based on carrying value with estimated refreshed FICO scores, No FICO available	0.80%	1.40%
Credit card | California
Loans and Leases Receivable Disclosure [Line Items]
Retained	$ 23,757	$ 22,245
Credit card | Texas
Loans and Leases Receivable Disclosure [Line Items]
Retained	15,085	14,200
Credit card | New York
Loans and Leases Receivable Disclosure [Line Items]
Retained	13,601	13,021
Credit card | Florida
Loans and Leases Receivable Disclosure [Line Items]
Retained	9,770	9,138
Credit card | Illinois
Loans and Leases Receivable Disclosure [Line Items]
Retained	8,938	8,585
Credit card | New Jersey
Loans and Leases Receivable Disclosure [Line Items]
Retained	6,739	6,506
Credit card | Ohio
Loans and Leases Receivable Disclosure [Line Items]
Retained	5,094	4,997
Credit card | Pennsylvania
Loans and Leases Receivable Disclosure [Line Items]
Retained	4,996	4,883
Credit card | Colorado
Loans and Leases Receivable Disclosure [Line Items]
Retained	4,309	4,006
Credit card | Michigan
Loans and Leases Receivable Disclosure [Line Items]
Retained	3,912	3,826
Credit card | All other
Loans and Leases Receivable Disclosure [Line Items]
Retained	60,415	57,980
Credit card | Current and less than 30 days past due and still accruing
Loans and Leases Receivable Disclosure [Line Items]
Retained	153,746	146,704
Credit card | 30–89 days past due and still accruing
Loans and Leases Receivable Disclosure [Line Items]
Retained	1,426	1,305
Credit card | 90 or more days past due and still accruing
Loans and Leases Receivable Disclosure [Line Items]
Retained	$ 1,444	$ 1,378