Loans and Allowance for Credit Losses - Additional Detail of Allowance for Credit Losses and Related Loan Balances by Portfolio Class (Detail) - USD ($) $ in Millions	Sep. 30, 2016	Jun. 30, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Dec. 31, 2014
Allowance Balance at End of Period
Loans individually evaluated for impairment	$ 58		$ 13
TDRs collectively evaluated for impairment	300		345
Other loans collectively evaluated for impairment	3,937		3,900
Loans acquired with deteriorated credit quality	43		48
Total allowance for credit losses	4,338	$ 4,329	4,306	$ 4,306	$ 4,326	$ 4,375
Loan Balance at End of Period
Loans individually evaluated for impairment	637		390
TDRs collectively evaluated for impairment	4,261		5,070
Other loans collectively evaluated for impairment	263,812		252,590
Loans acquired with deteriorated credit quality	2,579		2,799
Total loans	267,268		256,253
Total loans	271,289		260,849
Commercial [Member]
Allowance Balance at End of Period
Loans individually evaluated for impairment	56		11
TDRs collectively evaluated for impairment	10		10
Other loans collectively evaluated for impairment	1,410		1,266
Total allowance for credit losses	1,476	1,473	1,287	1,223	1,180	1,146
Loan Balance at End of Period
Loans individually evaluated for impairment	600		336
TDRs collectively evaluated for impairment	145		138
Other loans collectively evaluated for impairment	92,449		87,927
Loans acquired with deteriorated credit quality	7		1
Total loans	93,201		88,402
Commercial Real Estate [Member]
Allowance Balance at End of Period
Loans individually evaluated for impairment	2		2
TDRs collectively evaluated for impairment	4		7
Other loans collectively evaluated for impairment	765		703
Loans acquired with deteriorated credit quality	10		12
Total allowance for credit losses	781	748	724	736	735	726
Loan Balance at End of Period
Loans individually evaluated for impairment	37		41
TDRs collectively evaluated for impairment	165		235
Other loans collectively evaluated for impairment	43,016		41,566
Loans acquired with deteriorated credit quality	250		295
Total loans	43,468		42,137
Residential Mortgages [Member]
Allowance Balance at End of Period
TDRs collectively evaluated for impairment	195		236
Other loans collectively evaluated for impairment	325		395
Total allowance for credit losses	520	544	631	688	737	787
Loan Balance at End of Period
Loans individually evaluated for impairment			13
TDRs collectively evaluated for impairment	3,519		4,241
Other loans collectively evaluated for impairment	52,710		49,241
Loans acquired with deteriorated credit quality			1
Total loans	56,229		53,496
Other Retail [Member]
Allowance Balance at End of Period
TDRs collectively evaluated for impairment	28		33
Other loans collectively evaluated for impairment	598		710
Total allowance for credit losses	626	643	743	744	752	771
Loan Balance at End of Period
TDRs collectively evaluated for impairment	178		211
Other loans collectively evaluated for impairment	53,486		50,995
Total loans	53,664		51,206
Credit Card [Member]
Allowance Balance at End of Period
TDRs collectively evaluated for impairment	62		57
Other loans collectively evaluated for impairment	839		826
Total allowance for credit losses	901	884	883	876	873	880
Loan Balance at End of Period
TDRs collectively evaluated for impairment	217		210
Other loans collectively evaluated for impairment	20,489		20,802
Total loans	20,706		21,012
Total Loans, Excluding Covered Loans [Member]
Allowance Balance at End of Period
Loans individually evaluated for impairment	58		13
TDRs collectively evaluated for impairment	299		343
Other loans collectively evaluated for impairment	3,937		3,900
Loans acquired with deteriorated credit quality	10		12
Total allowance for credit losses	4,304	4,292	4,268	4,267	4,277	4,310
Loan Balance at End of Period
Loans individually evaluated for impairment	637		390
TDRs collectively evaluated for impairment	4,224		5,035
Other loans collectively evaluated for impairment	262,150		250,531
Loans acquired with deteriorated credit quality	257		297
Total loans	267,268		256,253
Covered Loans [Member]
Allowance Balance at End of Period
TDRs collectively evaluated for impairment	1		2
Loans acquired with deteriorated credit quality	33		36
Total allowance for credit losses	34	$ 37	38	$ 39	$ 49	$ 65
Loan Balance at End of Period
TDRs collectively evaluated for impairment	37		35
Other loans collectively evaluated for impairment	1,662		2,059
Loans acquired with deteriorated credit quality	2,322		2,502
Total loans	$ 4,021		$ 4,596