Asset Quality (Analysis of Loan Portfolio) (Details) - USD ($) $ in Millions	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	$ 220,458	[1]	$ 210,833	[1]	$ 206,696
Percentage Of Total Loans	100.00%		100.00%
Unearned income, net deferred loan fees, unamortized discounts and premiums, and purchase discounts and premiums	$ 1,200		$ 1,300
Current or Less Than 30 Days Past Due
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	$ 214,480		$ 203,938
Percentage Of Total Loans	97.29%		96.73%
30-59 Days Past Due
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	$ 545		$ 562
Percentage Of Total Loans	0.25%		0.27%
60-89 Days Past Due
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	$ 238		$ 232
Percentage Of Total Loans	0.11%		0.11%
90 Days or More Past Due
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	$ 737		$ 782
Percentage Of Total Loans	0.33%		0.37%
Total Past Due
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	$ 1,520		$ 1,576
Percentage Of Total Loans	0.69%		0.75%
Nonperforming Loans
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	$ 1,865		$ 2,144
Percentage Of Total Loans	0.85%		1.02%
Fair Value Option Nonaccrual Loans
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	$ 197		$ 219
Percentage Of Total Loans	0.09%		0.10%
Purchased Impaired Loans
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	$ 2,396		$ 2,956
Percentage Of Total Loans	1.08%		1.40%
Total commercial lending
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	$ 147,439		$ 137,955		133,544
Total commercial lending | Current or Less Than 30 Days Past Due
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	146,729		137,014
Total commercial lending | 30-59 Days Past Due
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	89		115
Total commercial lending | 60-89 Days Past Due
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	28		23
Total commercial lending | 90 Days or More Past Due
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	39		39
Total commercial lending | Total Past Due
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	156		177
Total commercial lending | Nonperforming Loans
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	554		655
Total commercial lending | Purchased Impaired Loans
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans			109
Total consumer lending
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	73,019		72,878		$ 73,152
Total consumer lending | Current or Less Than 30 Days Past Due
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	67,751		66,924
Total consumer lending | 30-59 Days Past Due
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	456		447
Total consumer lending | 60-89 Days Past Due
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	210		209
Total consumer lending | 90 Days or More Past Due
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	698		743
Total consumer lending | Total Past Due
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	1,364		1,399
Total consumer lending | Nonperforming Loans
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	1,311		1,489
Total consumer lending | Fair Value Option Nonaccrual Loans
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	197		219
Total consumer lending | Purchased Impaired Loans
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	2,396		2,847
Commercial | Total commercial lending
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	110,527		101,364
Commercial | Total commercial lending | Current or Less Than 30 Days Past Due
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	109,989		100,710
Commercial | Total commercial lending | 30-59 Days Past Due
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	45		81
Commercial | Total commercial lending | 60-89 Days Past Due
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	25		20
Commercial | Total commercial lending | 90 Days or More Past Due
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	39		39
Commercial | Total commercial lending | Total Past Due
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	109		140
Commercial | Total commercial lending | Nonperforming Loans
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	429		496
Commercial | Total commercial lending | Purchased Impaired Loans
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans			18
Commercial Real Estate | Total commercial lending
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	28,978		29,010
Commercial Real Estate | Total commercial lending | Current or Less Than 30 Days Past Due
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	28,826		28,769
Commercial Real Estate | Total commercial lending | 30-59 Days Past Due
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	27		5
Commercial Real Estate | Total commercial lending | 60-89 Days Past Due
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	2		2
Commercial Real Estate | Total commercial lending | 90 Days or More Past Due
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans
Commercial Real Estate | Total commercial lending | Total Past Due
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	29		7
Commercial Real Estate | Total commercial lending | Nonperforming Loans
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	123		143
Commercial Real Estate | Total commercial lending | Purchased Impaired Loans
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans			91
Equipment Lease Financing | Total commercial lending
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	7,934		7,581
Equipment Lease Financing | Total commercial lending | Current or Less Than 30 Days Past Due
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	7,914		7,535
Equipment Lease Financing | Total commercial lending | 30-59 Days Past Due
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	17		29
Equipment Lease Financing | Total commercial lending | 60-89 Days Past Due
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	1		1
Equipment Lease Financing | Total commercial lending | Total Past Due
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	18		30
Equipment Lease Financing | Total commercial lending | Nonperforming Loans
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	2		16
Home Equity | Total consumer lending
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	28,364		29,949
Home Equity | Total consumer lending | Current or Less Than 30 Days Past Due
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	26,561		27,820
Home Equity | Total consumer lending | 30-59 Days Past Due
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	78		64
Home Equity | Total consumer lending | 60-89 Days Past Due
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	26		30
Home Equity | Total consumer lending | Total Past Due
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	104		94
Home Equity | Total consumer lending | Nonperforming Loans
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	818		914
Home Equity | Total consumer lending | Purchased Impaired Loans
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	881		1,121
Residential Real Estate | Total consumer lending
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	17,212		15,598
Residential Real Estate | Total consumer lending | Current or Less Than 30 Days Past Due
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	14,389		12,425
Residential Real Estate | Total consumer lending | 30-59 Days Past Due
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	151		159
Residential Real Estate | Total consumer lending | 60-89 Days Past Due
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	74		68
Residential Real Estate | Total consumer lending | 90 Days or More Past Due
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	486		500
Residential Real Estate | Total consumer lending | Total Past Due
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	711		727
Residential Real Estate | Total consumer lending | Total Past Due | Government Insured or Guaranteed Loans
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	600		600
Residential Real Estate | Total consumer lending | Nonperforming Loans
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	400		501
Residential Real Estate | Total consumer lending | Fair Value Option Nonaccrual Loans
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	197		219
Residential Real Estate | Total consumer lending | Purchased Impaired Loans
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	1,515		1,726
Credit Card
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	5,699		5,282
Credit Card | Total consumer lending
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	5,699		5,282
Credit Card | Total consumer lending | Current or Less Than 30 Days Past Due
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	5,579		5,187
Credit Card | Total consumer lending | 30-59 Days Past Due
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	43		33
Credit Card | Total consumer lending | 60-89 Days Past Due
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	26		21
Credit Card | Total consumer lending | 90 Days or More Past Due
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	45		37
Credit Card | Total consumer lending | Total Past Due
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	114		91
Credit Card | Total consumer lending | Nonperforming Loans
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	6		4
Automobile | Total consumer lending | Other Consumer
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	12,880		12,380
Automobile | Total consumer lending | Current or Less Than 30 Days Past Due | Other Consumer
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	12,697		12,257
Automobile | Total consumer lending | 30-59 Days Past Due | Other Consumer
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	79		51
Automobile | Total consumer lending | 60-89 Days Past Due | Other Consumer
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	20		12
Automobile | Total consumer lending | 90 Days or More Past Due | Other Consumer
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	8		5
Automobile | Total consumer lending | Total Past Due | Other Consumer
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	107		68
Automobile | Total consumer lending | Nonperforming Loans | Other Consumer
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	76		55
Education and other | Total consumer lending | Other Consumer
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	8,864		9,669
Education and other | Total consumer lending | Current or Less Than 30 Days Past Due | Other Consumer
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	8,525		9,235
Education and other | Total consumer lending | 30-59 Days Past Due | Other Consumer
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	105		140
Education and other | Total consumer lending | 60-89 Days Past Due | Other Consumer
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	64		78
Education and other | Total consumer lending | 90 Days or More Past Due | Other Consumer
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	159		201
Education and other | Total consumer lending | Total Past Due | Other Consumer
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	328		419
Education and other | Total consumer lending | Total Past Due | Government Insured or Guaranteed Loans | Other Consumer
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	300		400
Education and other | Total consumer lending | Nonperforming Loans | Other Consumer
Financing Receivable. Recorded Investment, Past Due [Line Items]
Total Loans	$ 11		$ 15

[1] Our consolidated assets included the following for which we have elected the fair value option: Loans held for sale of $1.7 billion, Loans of $.9 billion, and Other assets of $.3 billion at December 31, 2017 and Loans held for sale of $2.4 billion, Loans of $.9 billion, and Other assets of $.5 billion at December 31, 2016.