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, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	$ 267,268	$ 256,253
Total loans	271,289	260,849
Total outstanding commitments	568,286	548,404
Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	264,694	255,014
Total outstanding commitments	557,554	539,614
Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,225	2,002
Total outstanding commitments	4,805	3,945
Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,370	3,833
Total outstanding commitments	5,927	4,845
Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	6,595	5,835
Total outstanding commitments	10,732	8,790
Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	93,201	88,402
Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	89,289	85,206
Commercial [Member] | Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	1,702	1,629
Commercial [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	2,210	1,567
Commercial [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	3,912	3,196
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	43,468	42,137
Commercial Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	42,204	41,079
Commercial Real Estate [Member] | Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	512	365
Commercial Real Estate [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	752	693
Commercial Real Estate [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	1,264	1,058
Residential Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	56,229	53,496
Residential Mortgages [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	55,394	52,548
Residential Mortgages [Member] | Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	6	2
Residential Mortgages [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	829	946
Residential Mortgages [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	835	948
Other Retail [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	53,664	51,206
Other Retail [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	53,387	50,899
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	272	301
Other Retail [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	277	307
Credit Card [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	20,706	21,012
Credit Card [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	20,474	20,775
Credit Card [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	232	237
Credit Card [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	232	237
Total Loans, Excluding Covered Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	267,268	256,253
Total Loans, Excluding Covered Loans [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	260,748	250,507
Total Loans, Excluding Covered Loans [Member] | Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	2,225	2,002
Total Loans, Excluding Covered Loans [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	4,295	3,744
Total Loans, Excluding Covered Loans [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	6,520	5,746
Covered Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,021	4,596
Covered Loans [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,946	4,507
Covered Loans [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	75	89
Covered Loans [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 75	$ 89