Loans and Allowance for Credit Losses - Summary of Loans by Portfolio Class and Company's Internal Credit Quality Rating (Detail) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	$ 274,932	$ 277,311
Total loans	277,911	280,432
Total outstanding commitments	593,354	591,201
Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	98,097	97,561
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	40,140	40,463
Residential Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	60,477	59,783
Other Retail [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	55,317	57,324
Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	273,170	275,576
Total outstanding commitments	586,609	584,072
Pass [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	95,757	95,297
Pass [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	38,990	39,162
Pass [Member] | Residential Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	59,855	59,141
Pass [Member] | Other Retail [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	55,005	57,009
Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,874	1,800
Total outstanding commitments	3,129	3,142
Special Mention Criticized [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	1,290	1,130
Special Mention Criticized [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	556	648
Special Mention Criticized [Member] | Residential Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	18	16
Special Mention Criticized [Member] | Other Retail [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	10	6
Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,867	3,056
Total outstanding commitments	3,616	3,987
Classified Criticized [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	1,050	1,134
Classified Criticized [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	594	653
Classified Criticized [Member] | Residential Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	604	626
Classified Criticized [Member] | Other Retail [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	302	309
Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,741	4,856
Total outstanding commitments	6,745	7,129
Total Criticized [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	2,340	2,264
Total Criticized [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	1,150	1,301
Total Criticized [Member] | Residential Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	622	642
Total Criticized [Member] | Other Retail [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	312	315
Credit Card [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	20,901	22,180
Credit Card [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	20,631	21,895
Credit Card [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	270	285
Credit Card [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	270	285
Total Loans, Excluding Covered Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	274,932	277,311
Total Loans, Excluding Covered Loans [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	270,238	272,504
Total Loans, Excluding Covered Loans [Member] | Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	1,874	1,800
Total Loans, Excluding Covered Loans [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	2,820	3,007
Total Loans, Excluding Covered Loans [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	4,694	4,807
Covered Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,979	3,121
Covered Loans [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,932	3,072
Covered Loans [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	47	49
Covered Loans [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 47	$ 49