Loans - Consumer, Excluding Credit Card Loan Portfolio, Other Consumer Loans (Details) - USD ($)	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 928,887,000,000	$ 969,415,000,000	$ 947,651,000,000
Consumer, excluding credit card
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	331,809,000,000	373,637,000,000	$ 375,958,000,000
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	$ 61,410,000,000	$ 63,573,000,000
% of 30 plus days past due to total retained loans	0.88%	0.93%
Nonaccrual loans	$ 112,000,000	$ 128,000,000
Consumer, excluding credit card | Auto | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	13,823,000,000	15,749,000,000
Consumer, excluding credit card | Auto | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	394,000,000	273,000,000
Consumer, excluding credit card | Auto | Criticized nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	0	0
Consumer, excluding credit card | Auto | California
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	8,016,000,000	8,330,000,000
Consumer, excluding credit card | Auto | Texas
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	6,644,000,000	6,531,000,000
Consumer, excluding credit card | Auto | New York
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	3,627,000,000	3,863,000,000
Consumer, excluding credit card | Auto | Illinois
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	3,438,000,000	3,716,000,000
Consumer, excluding credit card | Auto | Florida
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	3,280,000,000	3,256,000,000
Consumer, excluding credit card | Auto | Arizona
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	1,990,000,000	2,084,000,000
Consumer, excluding credit card | Auto | Ohio
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	1,900,000,000	1,973,000,000
Consumer, excluding credit card | Auto | New Jersey
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	1,920,000,000	1,981,000,000
Consumer, excluding credit card | Auto | Michigan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	1,279,000,000	1,357,000,000
Consumer, excluding credit card | Auto | Louisiana
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	1,598,000,000	1,587,000,000
Consumer, excluding credit card | Auto | All other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	27,718,000,000	28,895,000,000
Consumer, excluding credit card | Auto | Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	60,872,000,000	62,984,000,000
Consumer, excluding credit card | Auto | 30–119 days past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	534,000,000	589,000,000
Consumer, excluding credit card | Auto | 120 or more days past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	4,000,000	0
Consumer, excluding credit card | Consumer & Business Banking
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 26,699,000,000	$ 26,612,000,000
% of 30 plus days past due to total retained loans	1.32%	1.36%
Nonaccrual loans	$ 268,000,000	$ 245,000,000
Consumer, excluding credit card | Consumer & Business Banking | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	18,738,000,000	18,743,000,000
Consumer, excluding credit card | Consumer & Business Banking | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	747,000,000	751,000,000
Consumer, excluding credit card | Consumer & Business Banking | Criticized nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	218,000,000	191,000,000
Consumer, excluding credit card | Consumer & Business Banking | California
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	5,744,000,000	5,520,000,000
Consumer, excluding credit card | Consumer & Business Banking | Texas
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	3,042,000,000	2,993,000,000
Consumer, excluding credit card | Consumer & Business Banking | New York
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	4,339,000,000	4,381,000,000
Consumer, excluding credit card | Consumer & Business Banking | Illinois
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	1,737,000,000	2,046,000,000
Consumer, excluding credit card | Consumer & Business Banking | Florida
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	1,565,000,000	1,502,000,000
Consumer, excluding credit card | Consumer & Business Banking | Arizona
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	1,268,000,000	1,491,000,000
Consumer, excluding credit card | Consumer & Business Banking | Ohio
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	1,189,000,000	1,305,000,000
Consumer, excluding credit card | Consumer & Business Banking | New Jersey
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	805,000,000	723,000,000
Consumer, excluding credit card | Consumer & Business Banking | Michigan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	1,264,000,000	1,329,000,000
Consumer, excluding credit card | Consumer & Business Banking | Louisiana
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	768,000,000	860,000,000
Consumer, excluding credit card | Consumer & Business Banking | All other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	4,978,000,000	4,462,000,000
Consumer, excluding credit card | Consumer & Business Banking | Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	26,346,000,000	26,249,000,000
Consumer, excluding credit card | Consumer & Business Banking | 30–119 days past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	231,000,000	252,000,000
Consumer, excluding credit card | Consumer & Business Banking | 120 or more days past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	122,000,000	111,000,000
Consumer, excluding credit card | Total other consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 88,109,000,000	$ 90,185,000,000
% of 30 plus days past due to total retained loans	1.01%	1.06%
Nonaccrual loans	$ 380,000,000	$ 373,000,000
Consumer, excluding credit card | Total other consumer | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	32,561,000,000	34,492,000,000
Consumer, excluding credit card | Total other consumer | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	1,141,000,000	1,024,000,000
Consumer, excluding credit card | Total other consumer | Criticized nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	218,000,000	191,000,000
Consumer, excluding credit card | Total other consumer | California
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	13,760,000,000	13,850,000,000
Consumer, excluding credit card | Total other consumer | Texas
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	9,686,000,000	9,524,000,000
Consumer, excluding credit card | Total other consumer | New York
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	7,966,000,000	8,244,000,000
Consumer, excluding credit card | Total other consumer | Illinois
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	5,175,000,000	5,762,000,000
Consumer, excluding credit card | Total other consumer | Florida
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	4,845,000,000	4,758,000,000
Consumer, excluding credit card | Total other consumer | Arizona
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	3,258,000,000	3,575,000,000
Consumer, excluding credit card | Total other consumer | Ohio
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	3,089,000,000	3,278,000,000
Consumer, excluding credit card | Total other consumer | New Jersey
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	2,725,000,000	2,704,000,000
Consumer, excluding credit card | Total other consumer | Michigan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	2,543,000,000	2,686,000,000
Consumer, excluding credit card | Total other consumer | Louisiana
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	2,366,000,000	2,447,000,000
Consumer, excluding credit card | Total other consumer | All other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	32,696,000,000	33,357,000,000
Consumer, excluding credit card | Total other consumer | Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	87,218,000,000	89,233,000,000
Consumer, excluding credit card | Total other consumer | 30–119 days past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	765,000,000	841,000,000
Consumer, excluding credit card | Total other consumer | 120 or more days past due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 126,000,000	$ 111,000,000