Loans - Consumer, Excluding Credit Card Loan Portfolio, Other Consumer Loans (Details) - USD ($)	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 940,440,000,000	$ 924,838,000,000	$ 899,576,000,000
Consumer, excluding credit card
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	374,587,000,000	372,553,000,000	$ 365,115,000,000
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	$ 65,014,000,000	$ 66,242,000,000
% of 30 plus days past due to total retained loans	0.77%	0.89%
Nonaccrual loans	$ 124,000,000	$ 141,000,000
Consumer, excluding credit card | Auto | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	15,150,000,000	15,604,000,000
Consumer, excluding credit card | Auto | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	261,000,000	93,000,000
Consumer, excluding credit card | Auto | Criticized nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	7,000,000	9,000,000
Consumer, excluding credit card | Auto | California
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	8,512,000,000	8,445,000,000
Consumer, excluding credit card | Auto | Texas
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	6,675,000,000	7,013,000,000
Consumer, excluding credit card | Auto | New York
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	3,901,000,000	4,023,000,000
Consumer, excluding credit card | Auto | Illinois
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	3,793,000,000	3,916,000,000
Consumer, excluding credit card | Auto | Florida
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	3,389,000,000	3,350,000,000
Consumer, excluding credit card | Auto | Arizona
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	2,103,000,000	2,221,000,000
Consumer, excluding credit card | Auto | Ohio
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	2,044,000,000	2,105,000,000
Consumer, excluding credit card | Auto | Michigan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	1,417,000,000	1,418,000,000
Consumer, excluding credit card | Auto | New Jersey
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	1,978,000,000	2,044,000,000
Consumer, excluding credit card | Auto | Louisiana
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	1,602,000,000	1,656,000,000
Consumer, excluding credit card | Auto | All other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	29,600,000,000	30,051,000,000
Consumer, excluding credit card | Auto | Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	64,516,000,000	65,651,000,000
Consumer, excluding credit card | Auto | 30–119 days past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	487,000,000	584,000,000
Consumer, excluding credit card | Auto | 120 or more days past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	11,000,000	7,000,000
Consumer, excluding credit card | Consumer and Business Banking
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 26,272,000,000	$ 25,789,000,000
% of 30 plus days past due to total retained loans	1.17%	1.30%
Nonaccrual loans	$ 273,000,000	$ 283,000,000
Consumer, excluding credit card | Consumer and Business Banking | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	18,387,000,000	17,938,000,000
Consumer, excluding credit card | Consumer and Business Banking | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	759,000,000	791,000,000
Consumer, excluding credit card | Consumer and Business Banking | Criticized nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	204,000,000	213,000,000
Consumer, excluding credit card | Consumer and Business Banking | California
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	5,299,000,000	5,032,000,000
Consumer, excluding credit card | Consumer and Business Banking | Texas
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	3,014,000,000	2,916,000,000
Consumer, excluding credit card | Consumer and Business Banking | New York
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	4,222,000,000	4,195,000,000
Consumer, excluding credit card | Consumer and Business Banking | Illinois
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	2,066,000,000	2,017,000,000
Consumer, excluding credit card | Consumer and Business Banking | Florida
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	1,428,000,000	1,424,000,000
Consumer, excluding credit card | Consumer and Business Banking | Arizona
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	1,422,000,000	1,383,000,000
Consumer, excluding credit card | Consumer and Business Banking | Ohio
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	1,356,000,000	1,380,000,000
Consumer, excluding credit card | Consumer and Business Banking | Michigan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	1,304,000,000	1,357,000,000
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 | Louisiana
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	885,000,000	849,000,000
Consumer, excluding credit card | Consumer and Business Banking | All other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	4,538,000,000	4,515,000,000
Consumer, excluding credit card | Consumer and Business Banking | Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	25,964,000,000	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	197,000,000	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	111,000,000	122,000,000
Consumer, excluding credit card | Total other consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 91,286,000,000	$ 92,031,000,000
% of 30 plus days past due to total retained loans	0.88%	1.01%
Nonaccrual loans	$ 397,000,000	$ 424,000,000
Consumer, excluding credit card | Total other consumer | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	33,537,000,000	33,542,000,000
Consumer, excluding credit card | Total other consumer | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	1,020,000,000	884,000,000
Consumer, excluding credit card | Total other consumer | Criticized nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	211,000,000	222,000,000
Consumer, excluding credit card | Total other consumer | California
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	13,811,000,000	13,477,000,000
Consumer, excluding credit card | Total other consumer | Texas
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	9,689,000,000	9,929,000,000
Consumer, excluding credit card | Total other consumer | New York
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	8,123,000,000	8,218,000,000
Consumer, excluding credit card | Total other consumer | Illinois
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	5,859,000,000	5,933,000,000
Consumer, excluding credit card | Total other consumer | Florida
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	4,817,000,000	4,774,000,000
Consumer, excluding credit card | Total other consumer | Arizona
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	3,525,000,000	3,604,000,000
Consumer, excluding credit card | Total other consumer | Ohio
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	3,400,000,000	3,485,000,000
Consumer, excluding credit card | Total other consumer | Michigan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	2,721,000,000	2,775,000,000
Consumer, excluding credit card | Total other consumer | New Jersey
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	2,716,000,000	2,765,000,000
Consumer, excluding credit card | Total other consumer | Louisiana
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	2,487,000,000	2,505,000,000
Consumer, excluding credit card | Total other consumer | All other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	34,138,000,000	34,566,000,000
Consumer, excluding credit card | Total other consumer | Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	90,480,000,000	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	684,000,000	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	$ 122,000,000	$ 129,000,000