Loans and Allowance for Credit Losses - Additional Detail of Allowance for Credit Losses and Related Loan Balances by Portfolio Type (Detail) - USD ($) $ in Millions	Sep. 30, 2015	Jun. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Dec. 31, 2013
Allowance Balance at End of Period
Loans individually evaluated for impairment	$ 9		$ 9
TDRs collectively evaluated for impairment	393		449
Other loans collectively evaluated for impairment	3,854		3,825
Loans acquired with deteriorated credit quality	50		92
Total allowance for credit losses	4,306	$ 4,326	4,375	$ 4,414	$ 4,449	$ 4,537
Loan balance at end of period
Loans individually evaluated for impairment	322		299
TDRs collectively evaluated for impairment	5,241		5,681
Other loans collectively evaluated for impairment	246,333		238,555
Loans acquired with deteriorated credit quality	2,895		3,316
Total loans	250,000		242,570
Total loans	254,791		247,851
Commercial [Member]
Allowance Balance at End of Period
Loans individually evaluated for impairment	8		5
TDRs collectively evaluated for impairment	8		12
Other loans collectively evaluated for impairment	1,207		1,129
Total allowance for credit losses	1,223	1,180	1,146	1,136	1,111	1,075
Loan balance at end of period
Loans individually evaluated for impairment	267		159
TDRs collectively evaluated for impairment	136		124
Other loans collectively evaluated for impairment	85,135		80,093
Loans acquired with deteriorated credit quality	1		1
Total loans	85,539		80,377
Commercial Real Estate [Member]
Allowance Balance at End of Period
Loans individually evaluated for impairment	1		4
TDRs collectively evaluated for impairment	11		12
Other loans collectively evaluated for impairment	710		678
Loans acquired with deteriorated credit quality	14		32
Total allowance for credit losses	736	735	726	715	725	776
Loan balance at end of period
Loans individually evaluated for impairment	42		128
TDRs collectively evaluated for impairment	250		393
Other loans collectively evaluated for impairment	41,873		41,744
Loans acquired with deteriorated credit quality	313		530
Total loans	42,478		42,795
Residential Mortgages [Member]
Allowance Balance at End of Period
TDRs collectively evaluated for impairment	280		319
Other loans collectively evaluated for impairment	408		468
Total allowance for credit losses	688	737	787	793	848	875
Loan balance at end of period
Loans individually evaluated for impairment	13		12
TDRs collectively evaluated for impairment	4,387		4,653
Other loans collectively evaluated for impairment	47,948		46,953
Loans acquired with deteriorated credit quality	1		1
Total loans	52,349		51,619
Credit Card [Member]
Allowance Balance at End of Period
TDRs collectively evaluated for impairment	56		61
Other loans collectively evaluated for impairment	820		819
Total allowance for credit losses	876	873	880	878	874	884
Loan balance at end of period
TDRs collectively evaluated for impairment	214		240
Other loans collectively evaluated for impairment	18,369		18,275
Total loans	18,583		18,515
Other Retail [Member]
Allowance Balance at End of Period
TDRs collectively evaluated for impairment	36		41
Other loans collectively evaluated for impairment	708		730
Total allowance for credit losses	744	752	771	790	779	781
Loan balance at end of period
TDRs collectively evaluated for impairment	219		237
Other loans collectively evaluated for impairment	50,832		49,027
Total loans	51,051		49,264
Total Loans, Excluding Covered Loans [Member]
Allowance Balance at End of Period
Loans individually evaluated for impairment	9		9
TDRs collectively evaluated for impairment	391		445
Other loans collectively evaluated for impairment	3,853		3,824
Loans acquired with deteriorated credit quality	14		32
Total allowance for credit losses	4,267	4,277	4,310	4,312	4,337	4,391
Loan balance at end of period
Loans individually evaluated for impairment	322		299
TDRs collectively evaluated for impairment	5,206		5,647
Other loans collectively evaluated for impairment	244,157		236,092
Loans acquired with deteriorated credit quality	315		532
Total loans	250,000		242,570
Covered Loans [Member]
Allowance Balance at End of Period
TDRs collectively evaluated for impairment	2		4
Other loans collectively evaluated for impairment	1		1
Loans acquired with deteriorated credit quality	36		60
Total allowance for credit losses	39	$ 49	65	$ 102	$ 112	$ 146
Loan balance at end of period
TDRs collectively evaluated for impairment	35		34
Other loans collectively evaluated for impairment	2,176		2,463
Loans acquired with deteriorated credit quality	2,580		2,784
Total loans	$ 4,791		$ 5,281