Loans and Allowance for Credit Losses - Summary of Loans by Portfolio Class and Company's Internal Credit Quality Rating (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	$ 275,457	$ 269,371
Total loans	278,719	273,207
Total outstanding commitments	587,544	573,253
Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	273,243	266,665
Total outstanding commitments	579,628	562,704
Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,976	2,400
Total outstanding commitments	3,232	4,920
Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,500	4,142
Total outstanding commitments	4,684	5,629
Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	5,476	6,542
Total outstanding commitments	7,916	10,549
Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	96,928	93,386
Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	94,127	89,739
Commercial [Member] | Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	1,328	1,721
Commercial [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	1,473	1,926
Commercial [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	2,801	3,647
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	41,430	43,098
Commercial Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	39,998	41,634
Commercial Real Estate [Member] | Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	640	663
Commercial Real Estate [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	792	801
Commercial Real Estate [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	1,432	1,464
Residential Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	59,317	57,274
Residential Mortgages [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	58,671	56,457
Residential Mortgages [Member] | Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	3	10
Residential Mortgages [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	643	807
Residential Mortgages [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	646	817
Other Retail [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	56,859	53,864
Other Retail [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	56,567	53,576
Other Retail [Member] | Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	5	6
Other Retail [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	287	282
Other Retail [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	292	288
Credit Card [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	20,923	21,749
Credit Card [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	20,671	21,493
Credit Card [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	252	256
Credit Card [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	252	256
Total Loans, Excluding Covered Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	275,457	269,371
Total Loans, Excluding Covered Loans [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	270,034	262,899
Total Loans, Excluding Covered Loans [Member] | Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	1,976	2,400
Total Loans, Excluding Covered Loans [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	3,447	4,072
Total Loans, Excluding Covered Loans [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	5,423	6,472
Covered Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,262	3,836
Covered Loans [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,209	3,766
Covered Loans [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	53	70
Covered Loans [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 53	$ 70