Loans and Allowance for Credit Losses, Loans by Delinquency Status, Commercial (Details) - USD ($) $ in Millions		Sep. 30, 2018	Dec. 31, 2017	Dec. 31, 2008
By delinquency status:
Loans	[1]	$ 942,300	$ 956,770
Total Commercial [Member]
By delinquency status:
Loans		501,886	503,388
Commercial and Industrial Loans [Member]
By delinquency status:
Loans		338,048	333,125
Commercial real estate mortgage [Member]
By delinquency status:
Loans		120,403	126,599
Commercial Real Estate Construction [Member]
By delinquency status:
Loans		23,690	24,279
Commercial Lease Financing Receivable [Member]
By delinquency status:
Loans		19,745	19,385
Loans Excluding Purchased Credit-Impaired Loans [Member]
By delinquency status:
Over 90 DPD and still accruing		9,209	11,997
Nonaccrual loans		7,053	8,036
Loans Excluding Purchased Credit-Impaired Loans [Member] | Total Commercial [Member]
By delinquency status:
Loans		501,841	503,302
Nonaccrual loans		2,298	2,640
Loans Excluding Purchased Credit-Impaired Loans [Member] | Commercial and Industrial Loans [Member]
By delinquency status:
Loans		338,003	333,039
Nonaccrual loans		1,555	1,899
Loans Excluding Purchased Credit-Impaired Loans [Member] | Commercial real estate mortgage [Member]
By delinquency status:
Loans		120,403	126,599
Nonaccrual loans		603	628
Loans Excluding Purchased Credit-Impaired Loans [Member] | Commercial Real Estate Construction [Member]
By delinquency status:
Loans		23,690	24,279
Nonaccrual loans		44	37
Loans Excluding Purchased Credit-Impaired Loans [Member] | Commercial Lease Financing Receivable [Member]
By delinquency status:
Loans		19,745	19,385
Nonaccrual loans		96	76
PCI Loans Carrying Value [Member]
By delinquency status:
PCI loans		6,941	12,835
PCI Loans Carrying Value [Member] | Total Commercial [Member]
By delinquency status:
PCI loans		45	86	$ 18,700
PCI Loans Carrying Value [Member] | Commercial and Industrial Loans [Member]
By delinquency status:
PCI loans		45	86
PCI Loans Carrying Value [Member] | Commercial real estate mortgage [Member]
By delinquency status:
PCI loans		0	0
PCI Loans Carrying Value [Member] | Commercial Real Estate Construction [Member]
By delinquency status:
PCI loans		0	0
PCI Loans Carrying Value [Member] | Commercial Lease Financing Receivable [Member]
By delinquency status:
PCI loans		0	0
Pass [Member] | Loans Excluding Purchased Credit-Impaired Loans [Member] | Total Commercial [Member]
By delinquency status:
Loans		480,404	480,886
Pass [Member] | Loans Excluding Purchased Credit-Impaired Loans [Member] | Commercial and Industrial Loans [Member]
By delinquency status:
Loans		322,264	316,431
Pass [Member] | Loans Excluding Purchased Credit-Impaired Loans [Member] | Commercial real estate mortgage [Member]
By delinquency status:
Loans		115,970	122,312
Pass [Member] | Loans Excluding Purchased Credit-Impaired Loans [Member] | Commercial Real Estate Construction [Member]
By delinquency status:
Loans		23,419	23,981
Pass [Member] | Loans Excluding Purchased Credit-Impaired Loans [Member] | Commercial Lease Financing Receivable [Member]
By delinquency status:
Loans		18,751	18,162
Criticized [Member] | Loans Excluding Purchased Credit-Impaired Loans [Member] | Total Commercial [Member]
By delinquency status:
Loans		21,437	22,416
Criticized [Member] | Loans Excluding Purchased Credit-Impaired Loans [Member] | Commercial and Industrial Loans [Member]
By delinquency status:
Loans		15,739	16,608
Criticized [Member] | Loans Excluding Purchased Credit-Impaired Loans [Member] | Commercial real estate mortgage [Member]
By delinquency status:
Loans		4,433	4,287
Criticized [Member] | Loans Excluding Purchased Credit-Impaired Loans [Member] | Commercial Real Estate Construction [Member]
By delinquency status:
Loans		271	298
Criticized [Member] | Loans Excluding Purchased Credit-Impaired Loans [Member] | Commercial Lease Financing Receivable [Member]
By delinquency status:
Loans		994	1,223
Current-29 days past due (DPD) and still accruing [Member] | Loans Excluding Purchased Credit-Impaired Loans [Member] | Total Commercial [Member]
By delinquency status:
Loans		498,449	499,216
Current-29 days past due (DPD) and still accruing [Member] | Loans Excluding Purchased Credit-Impaired Loans [Member] | Commercial and Industrial Loans [Member]
By delinquency status:
Loans		336,004	330,319
Current-29 days past due (DPD) and still accruing [Member] | Loans Excluding Purchased Credit-Impaired Loans [Member] | Commercial real estate mortgage [Member]
By delinquency status:
Loans		119,445	125,642
Current-29 days past due (DPD) and still accruing [Member] | Loans Excluding Purchased Credit-Impaired Loans [Member] | Commercial Real Estate Construction [Member]
By delinquency status:
Loans		23,506	24,107
Current-29 days past due (DPD) and still accruing [Member] | Loans Excluding Purchased Credit-Impaired Loans [Member] | Commercial Lease Financing Receivable [Member]
By delinquency status:
Loans		19,494	19,148
30-89 days past due and still accruing [Member] | Loans Excluding Purchased Credit-Impaired Loans [Member] | Total Commercial [Member]
By delinquency status:
Loans		996	1,397
30-89 days past due and still accruing [Member] | Loans Excluding Purchased Credit-Impaired Loans [Member] | Commercial and Industrial Loans [Member]
By delinquency status:
Loans		402	795
30-89 days past due and still accruing [Member] | Loans Excluding Purchased Credit-Impaired Loans [Member] | Commercial real estate mortgage [Member]
By delinquency status:
Loans		299	306
30-89 days past due and still accruing [Member] | Loans Excluding Purchased Credit-Impaired Loans [Member] | Commercial Real Estate Construction [Member]
By delinquency status:
Loans		140	135
30-89 days past due and still accruing [Member] | Loans Excluding Purchased Credit-Impaired Loans [Member] | Commercial Lease Financing Receivable [Member]
By delinquency status:
Loans		155	161
Loans Excluding Government Insured or Guaranteed Loans [Member] | Loans Excluding Purchased Credit-Impaired Loans [Member]
By delinquency status:
Over 90 DPD and still accruing		933	1,063
Loans Excluding Government Insured or Guaranteed Loans [Member] | Loans Excluding Purchased Credit-Impaired Loans [Member] | Total Commercial [Member]
By delinquency status:
Over 90 DPD and still accruing		98	49
Loans Excluding Government Insured or Guaranteed Loans [Member] | Loans Excluding Purchased Credit-Impaired Loans [Member] | Commercial and Industrial Loans [Member]
By delinquency status:
Over 90 DPD and still accruing		42	26
Loans Excluding Government Insured or Guaranteed Loans [Member] | Loans Excluding Purchased Credit-Impaired Loans [Member] | Commercial real estate mortgage [Member]
By delinquency status:
Over 90 DPD and still accruing		56	23
Loans Excluding Government Insured or Guaranteed Loans [Member] | Loans Excluding Purchased Credit-Impaired Loans [Member] | Commercial Real Estate Construction [Member]
By delinquency status:
Over 90 DPD and still accruing		0	0
Loans Excluding Government Insured or Guaranteed Loans [Member] | Loans Excluding Purchased Credit-Impaired Loans [Member] | Commercial Lease Financing Receivable [Member]
By delinquency status:
Over 90 DPD and still accruing		$ 0	$ 0

[1] (3)Parenthetical amounts represent assets and liabilities for which we are required to carry at fair value or have elected the fair value option.