Loans and Allowance for Credit Losses - Summary of Loans by Portfolio Class and Company's Internal Credit Quality Rating (Detail) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	$ 277,354	$ 277,311
Total loans	280,177	280,432
Total outstanding commitments	596,926	591,201
Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	99,357	97,561
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	39,399	40,463
Residential Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	61,309	59,783
Other Retail [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	55,723	57,324
Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	275,643	275,576
Total outstanding commitments	591,015	584,072
Pass [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	97,207	95,297
Pass [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	38,192	39,162
Pass [Member] | Residential Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	60,738	59,141
Pass [Member] | Other Retail [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	55,409	57,009
Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,782	1,800
Total outstanding commitments	2,462	3,142
Special Mention Criticized [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	1,216	1,130
Special Mention Criticized [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	543	648
Special Mention Criticized [Member] | Residential Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	14	16
Special Mention Criticized [Member] | Other Retail [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	9	6
Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,752	3,056
Total outstanding commitments	3,449	3,987
Classified Criticized [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	934	1,134
Classified Criticized [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	664	653
Classified Criticized [Member] | Residential Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	557	626
Classified Criticized [Member] | Other Retail [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	305	309
Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,534	4,856
Total outstanding commitments	5,911	7,129
Total Criticized [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	2,150	2,264
Total Criticized [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	1,207	1,301
Total Criticized [Member] | Residential Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	571	642
Total Criticized [Member] | Other Retail [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	314	315
Credit Card [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	21,566	22,180
Credit Card [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	21,317	21,895
Credit Card [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	249	285
Credit Card [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	249	285
Total Loans, Excluding Covered Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	277,354	277,311
Total Loans, Excluding Covered Loans [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	272,863	272,504
Total Loans, Excluding Covered Loans [Member] | Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	1,782	1,800
Total Loans, Excluding Covered Loans [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	2,709	3,007
Total Loans, Excluding Covered Loans [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	4,491	4,807
Covered Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,823	3,121
Covered Loans [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,780	3,072
Covered Loans [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	43	49
Covered Loans [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 43	$ 49