Loans - Consumer, Excluding Credit Card Loan Portfolio, Other Consumer Loans (Details) - USD ($)	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 947,651,000,000	$ 924,838,000,000	$ 909,182,000,000
Consumer, excluding credit card
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	375,958,000,000	372,553,000,000	$ 369,413,000,000
90 or more days past due and still accruing	0	0
Consumer, excluding credit card | Auto
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 63,619,000,000	$ 66,242,000,000
% of 30 plus days past due to total retained loans	0.82%	0.89%
Nonaccrual loans	$ 137,000,000	$ 141,000,000
Consumer, excluding credit card | Auto | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	14,193,000,000	15,604,000,000
Consumer, excluding credit card | Auto | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	337,000,000	93,000,000
Consumer, excluding credit card | Auto | Criticized nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	3,000,000	9,000,000
Consumer, excluding credit card | Auto | California
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	8,382,000,000	8,445,000,000
Consumer, excluding credit card | Auto | Texas
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	6,497,000,000	7,013,000,000
Consumer, excluding credit card | Auto | New York
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	3,843,000,000	4,023,000,000
Consumer, excluding credit card | Auto | Illinois
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	3,667,000,000	3,916,000,000
Consumer, excluding credit card | Auto | Florida
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	3,332,000,000	3,350,000,000
Consumer, excluding credit card | Auto | Arizona
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	2,061,000,000	2,221,000,000
Consumer, excluding credit card | Auto | Ohio
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	1,987,000,000	2,105,000,000
Consumer, excluding credit card | Auto | New Jersey
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	1,990,000,000	2,044,000,000
Consumer, excluding credit card | Auto | Michigan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	1,378,000,000	1,418,000,000
Consumer, excluding credit card | Auto | Louisiana
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	1,570,000,000	1,656,000,000
Consumer, excluding credit card | Auto | All other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	28,912,000,000	30,051,000,000
Consumer, excluding credit card | Auto | Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	63,095,000,000	65,651,000,000
Consumer, excluding credit card | Auto | 30–119 days past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	517,000,000	584,000,000
Consumer, excluding credit card | Auto | 120 or more days past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	7,000,000	7,000,000
Consumer, excluding credit card | Consumer and Business Banking
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 26,451,000,000	$ 25,789,000,000
% of 30 plus days past due to total retained loans	1.06%	1.30%
Nonaccrual loans	$ 237,000,000	$ 283,000,000
Consumer, excluding credit card | Consumer and Business Banking | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	18,644,000,000	17,938,000,000
Consumer, excluding credit card | Consumer and Business Banking | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	760,000,000	791,000,000
Consumer, excluding credit card | Consumer and Business Banking | Criticized nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	195,000,000	213,000,000
Consumer, excluding credit card | Consumer and Business Banking | California
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	5,375,000,000	5,032,000,000
Consumer, excluding credit card | Consumer and Business Banking | Texas
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	3,002,000,000	2,916,000,000
Consumer, excluding credit card | Consumer and Business Banking | New York
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	4,218,000,000	4,195,000,000
Consumer, excluding credit card | Consumer and Business Banking | Illinois
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	2,045,000,000	2,017,000,000
Consumer, excluding credit card | Consumer and Business Banking | Florida
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	1,484,000,000	1,424,000,000
Consumer, excluding credit card | Consumer and Business Banking | Arizona
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	1,451,000,000	1,383,000,000
Consumer, excluding credit card | Consumer and Business Banking | Ohio
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	1,346,000,000	1,380,000,000
Consumer, excluding credit card | Consumer and Business Banking | New Jersey
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	738,000,000	721,000,000
Consumer, excluding credit card | Consumer and Business Banking | Michigan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	1,332,000,000	1,357,000,000
Consumer, excluding credit card | Consumer and Business Banking | Louisiana
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	860,000,000	849,000,000
Consumer, excluding credit card | Consumer and Business Banking | All other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	4,600,000,000	4,515,000,000
Consumer, excluding credit card | Consumer and Business Banking | Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	26,170,000,000	25,454,000,000
Consumer, excluding credit card | Consumer and Business Banking | 30–119 days past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	183,000,000	213,000,000
Consumer, excluding credit card | Consumer and Business Banking | 120 or more days past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	98,000,000	122,000,000
Consumer, excluding credit card | Total other consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 90,070,000,000	$ 92,031,000,000
% of 30 plus days past due to total retained loans	0.89%	1.01%
Nonaccrual loans	$ 374,000,000	$ 424,000,000
Consumer, excluding credit card | Total other consumer | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	32,837,000,000	33,542,000,000
Consumer, excluding credit card | Total other consumer | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	1,097,000,000	884,000,000
Consumer, excluding credit card | Total other consumer | Criticized nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	198,000,000	222,000,000
Consumer, excluding credit card | Total other consumer | California
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	13,757,000,000	13,477,000,000
Consumer, excluding credit card | Total other consumer | Texas
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	9,499,000,000	9,929,000,000
Consumer, excluding credit card | Total other consumer | New York
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	8,061,000,000	8,218,000,000
Consumer, excluding credit card | Total other consumer | Illinois
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	5,712,000,000	5,933,000,000
Consumer, excluding credit card | Total other consumer | Florida
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	4,816,000,000	4,774,000,000
Consumer, excluding credit card | Total other consumer | Arizona
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	3,512,000,000	3,604,000,000
Consumer, excluding credit card | Total other consumer | Ohio
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	3,333,000,000	3,485,000,000
Consumer, excluding credit card | Total other consumer | New Jersey
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	2,728,000,000	2,765,000,000
Consumer, excluding credit card | Total other consumer | Michigan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	2,710,000,000	2,775,000,000
Consumer, excluding credit card | Total other consumer | Louisiana
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	2,430,000,000	2,505,000,000
Consumer, excluding credit card | Total other consumer | All other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	33,512,000,000	34,566,000,000
Consumer, excluding credit card | Total other consumer | Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	89,265,000,000	91,105,000,000
Consumer, excluding credit card | Total other consumer | 30–119 days past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	700,000,000	797,000,000
Consumer, excluding credit card | Total other consumer | 120 or more days past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 105,000,000	$ 129,000,000