Loans and Allowance for Credit Losses - Summary of Loans by Portfolio Type and Company's Internal Credit Quality Rating (Detail) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	$ 264,287	$ 256,253
Total loans	268,521	260,849
Total outstanding commitments	563,641	548,404
Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	261,828	255,014
Total outstanding commitments	552,444	539,614
Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,226	2,002
Total outstanding commitments	5,227	3,945
Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,467	3,833
Total outstanding commitments	5,970	4,845
Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	6,693	5,835
Total outstanding commitments	11,197	8,790
Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	92,514	88,402
Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	88,383	85,206
Commercial [Member] | Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	1,766	1,629
Commercial [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	2,365	1,567
Commercial [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	4,131	3,196
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	43,290	42,137
Commercial Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	42,121	41,079
Commercial Real Estate [Member] | Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	452	365
Commercial Real Estate [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	717	693
Commercial Real Estate [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	1,169	1,058
Residential Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	55,904	53,496
Residential Mortgages [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	55,063	52,548
Residential Mortgages [Member] | Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	4	2
Residential Mortgages [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	837	946
Residential Mortgages [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	841	948
Other Retail [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	52,008	51,206
Other Retail [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	51,741	50,899
Other Retail [Member] | Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	4	6
Other Retail [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	263	301
Other Retail [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	267	307
Credit Card [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	20,571	21,012
Credit Card [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	20,365	20,775
Credit Card [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	206	237
Credit Card [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	206	237
Total Loans, Excluding Covered Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	264,287	256,253
Total Loans, Excluding Covered Loans [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	257,673	250,507
Total Loans, Excluding Covered Loans [Member] | Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	2,226	2,002
Total Loans, Excluding Covered Loans [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	4,388	3,744
Total Loans, Excluding Covered Loans [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	6,614	5,746
Covered Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,234	4,596
Covered Loans [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,155	4,507
Covered Loans [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	79	89
Covered Loans [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 79	$ 89