Loans and Allowance for Credit Losses - Additional Detail of Allowance for Credit Losses and Related Loan Balances by Portfolio Class (Detail) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Allowance Balance at End of Period
Loans individually evaluated for impairment	$ 31	$ 27
TDRs collectively evaluated for impairment	231	237
Other loans collectively evaluated for impairment	4,126	4,118
Loans acquired with deteriorated credit quality	29	35
Total allowance for credit losses	4,417	4,417	$ 4,366	$ 4,357
Loan Balance at End of Period
Loans individually evaluated for impairment	377	408
TDRs collectively evaluated for impairment	4,095	4,269
Other loans collectively evaluated for impairment	271,414	273,669
Loans acquired with deteriorated credit quality	2,025	2,086
Total loans	274,932	277,311
Total loans	277,911	280,432
Commercial [Member]
Allowance Balance at End of Period
Loans individually evaluated for impairment	28	23
TDRs collectively evaluated for impairment	12	14
Other loans collectively evaluated for impairment	1,346	1,335
Total allowance for credit losses	1,386	1,372	1,429	1,450
Loan Balance at End of Period
Loans individually evaluated for impairment	327	337
TDRs collectively evaluated for impairment	154	148
Other loans collectively evaluated for impairment	97,616	97,076
Total loans	98,097	97,561
Commercial Real Estate [Member]
Allowance Balance at End of Period
Loans individually evaluated for impairment	3	4
TDRs collectively evaluated for impairment	5	4
Other loans collectively evaluated for impairment	815	818
Loans acquired with deteriorated credit quality	3	5
Total allowance for credit losses	826	831	842	812
Loan Balance at End of Period
Loans individually evaluated for impairment	50	71
TDRs collectively evaluated for impairment	151	145
Other loans collectively evaluated for impairment	39,881	40,174
Loans acquired with deteriorated credit quality	58	73
Total loans	40,140	40,463
Residential Mortgages [Member]
Allowance Balance at End of Period
TDRs collectively evaluated for impairment	138	139
Other loans collectively evaluated for impairment	305	310
Total allowance for credit losses	443	449	485	510
Loan Balance at End of Period
TDRs collectively evaluated for impairment	3,339	3,524
Other loans collectively evaluated for impairment	57,137	56,258
Loans acquired with deteriorated credit quality	1	1
Total loans	60,477	59,783
Other Retail [Member]
Allowance Balance at End of Period
TDRs collectively evaluated for impairment	16	19
Other loans collectively evaluated for impairment	656	659
Total allowance for credit losses	672	678	622	617
Loan Balance at End of Period
TDRs collectively evaluated for impairment	181	186
Other loans collectively evaluated for impairment	55,136	57,138
Total loans	55,317	57,324
Credit Card [Member]
Allowance Balance at End of Period
TDRs collectively evaluated for impairment	60	60
Other loans collectively evaluated for impairment	1,004	996
Total allowance for credit losses	1,064	1,056	955	934
Loan Balance at End of Period
TDRs collectively evaluated for impairment	234	230
Other loans collectively evaluated for impairment	20,667	21,950
Total loans	20,901	22,180
Total Loans, Excluding Covered Loans [Member]
Allowance Balance at End of Period
Loans individually evaluated for impairment	31	27
TDRs collectively evaluated for impairment	231	236
Other loans collectively evaluated for impairment	4,126	4,118
Loans acquired with deteriorated credit quality	3	5
Total allowance for credit losses	4,391	4,386	4,333	4,323
Loan Balance at End of Period
Loans individually evaluated for impairment	377	408
TDRs collectively evaluated for impairment	4,059	4,233
Other loans collectively evaluated for impairment	270,437	272,596
Loans acquired with deteriorated credit quality	59	74
Total loans	274,932	277,311
Covered Loans [Member]
Allowance Balance at End of Period
TDRs collectively evaluated for impairment		1
Loans acquired with deteriorated credit quality	26	30
Total allowance for credit losses	26	31	$ 33	$ 34
Loan Balance at End of Period
TDRs collectively evaluated for impairment	36	36
Other loans collectively evaluated for impairment	977	1,073
Loans acquired with deteriorated credit quality	1,966	2,012
Total loans	$ 2,979	$ 3,121