Loans and Allowance for Credit Losses - Summary of Loans by Portfolio Type and Company's Internal Credit Quality Rating (Detail) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	$ 250,000	$ 242,570
Total loans	254,791	247,851
Total outstanding commitments	531,419	508,678
Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	249,066	242,581
Total outstanding commitments	523,370	501,535
Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,139	1,680
Total outstanding commitments	3,820	2,964
Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,586	3,590
Total outstanding commitments	4,229	4,179
Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	5,725	5,270
Total outstanding commitments	8,049	7,143
Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	85,539	80,377
Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	82,468	78,409
Commercial [Member] | Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	1,803	1,204
Commercial [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	1,268	764
Commercial [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	3,071	1,968
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	42,478	42,795
Commercial Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	41,411	41,322
Commercial Real Estate [Member] | Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	324	451
Commercial Real Estate [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	743	1,022
Commercial Real Estate [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	1,067	1,473
Residential Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	52,349	51,619
Residential Mortgages [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	51,375	50,479
Residential Mortgages [Member] | Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	7	5
Residential Mortgages [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	967	1,135
Residential Mortgages [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	974	1,140
Credit Card [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	18,583	18,515
Credit Card [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	18,367	18,275
Credit Card [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	216	240
Credit Card [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	216	240
Other Retail [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	51,051	49,264
Other Retail [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	50,749	48,932
Other Retail [Member] | Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	5	20
Other Retail [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	297	312
Other Retail [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	302	332
Total Loans, Excluding Covered Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	250,000	242,570
Total Loans, Excluding Covered Loans [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	244,370	237,417
Total Loans, Excluding Covered Loans [Member] | Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	2,139	1,680
Total Loans, Excluding Covered Loans [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	3,491	3,473
Total Loans, Excluding Covered Loans [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans, excluding covered loans	5,630	5,153
Covered Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,791	5,281
Covered Loans [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,696	5,164
Covered Loans [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	95	117
Covered Loans [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 95	$ 117