Loans and Allowance for Credit Losses - Additional Detail of Allowance for Credit Losses and Related Loan Balances by Portfolio Class (Detail) - USD ($) $ in Millions	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016
Allowance Balance at End of Period
Loans individually evaluated for impairment	$ 22		$ 27
TDRs collectively evaluated for impairment	231		237
Other loans collectively evaluated for impairment	4,133		4,118
Loans acquired with deteriorated credit quality	25		35
Total allowance for credit losses	4,411	$ 4,417	4,417	$ 4,377	$ 4,366	$ 4,357
Loan Balance at End of Period
Loans individually evaluated for impairment	325		408
TDRs collectively evaluated for impairment	4,121		4,269
Other loans collectively evaluated for impairment	273,781		273,669
Loans acquired with deteriorated credit quality	1,950		2,086
Total loans	277,354		277,311
Total loans	280,177		280,432
Commercial [Member]
Allowance Balance at End of Period
Loans individually evaluated for impairment	19		23
TDRs collectively evaluated for impairment	14		14
Other loans collectively evaluated for impairment	1,358		1,335
Total allowance for credit losses	1,391	1,386	1,372	1,395	1,429	1,450
Loan Balance at End of Period
Loans individually evaluated for impairment	272		337
TDRs collectively evaluated for impairment	158		148
Other loans collectively evaluated for impairment	98,927		97,076
Total loans	99,357		97,561
Commercial Real Estate [Member]
Allowance Balance at End of Period
Loans individually evaluated for impairment	3		4
TDRs collectively evaluated for impairment	3		4
Other loans collectively evaluated for impairment	803		818
Loans acquired with deteriorated credit quality	3		5
Total allowance for credit losses	812	826	831	856	842	812
Loan Balance at End of Period
Loans individually evaluated for impairment	53		71
TDRs collectively evaluated for impairment	135		145
Other loans collectively evaluated for impairment	39,175		40,174
Loans acquired with deteriorated credit quality	36		73
Total loans	39,399		40,463
Residential Mortgages [Member]
Allowance Balance at End of Period
TDRs collectively evaluated for impairment	136		139
Other loans collectively evaluated for impairment	300		310
Total allowance for credit losses	436	443	449	455	485	510
Loan Balance at End of Period
TDRs collectively evaluated for impairment	3,377		3,524
Other loans collectively evaluated for impairment	57,931		56,258
Loans acquired with deteriorated credit quality	1		1
Total loans	61,309		59,783
Other Retail [Member]
Allowance Balance at End of Period
TDRs collectively evaluated for impairment	16		19
Other loans collectively evaluated for impairment	651		659
Total allowance for credit losses	667	672	678	648	622	617
Loan Balance at End of Period
TDRs collectively evaluated for impairment	184		186
Other loans collectively evaluated for impairment	55,539		57,138
Total loans	55,723		57,324
Credit Card [Member]
Allowance Balance at End of Period
TDRs collectively evaluated for impairment	61		60
Other loans collectively evaluated for impairment	1,021		996
Total allowance for credit losses	1,082	1,064	1,056	990	955	934
Loan Balance at End of Period
TDRs collectively evaluated for impairment	233		230
Other loans collectively evaluated for impairment	21,333		21,950
Total loans	21,566		22,180
Total Loans, Excluding Covered Loans [Member]
Allowance Balance at End of Period
Loans individually evaluated for impairment	22		27
TDRs collectively evaluated for impairment	230		236
Other loans collectively evaluated for impairment	4,133		4,118
Loans acquired with deteriorated credit quality	3		5
Total allowance for credit losses	4,388	4,391	4,386	4,344	4,333	4,323
Loan Balance at End of Period
Loans individually evaluated for impairment	325		408
TDRs collectively evaluated for impairment	4,087		4,233
Other loans collectively evaluated for impairment	272,905		272,596
Loans acquired with deteriorated credit quality	37		74
Total loans	277,354		277,311
Covered Loans [Member]
Allowance Balance at End of Period
TDRs collectively evaluated for impairment	1		1
Loans acquired with deteriorated credit quality	22		30
Total allowance for credit losses	23	$ 26	31	$ 33	$ 33	$ 34
Loan Balance at End of Period
TDRs collectively evaluated for impairment	34		36
Other loans collectively evaluated for impairment	876		1,073
Loans acquired with deteriorated credit quality	1,913		2,012
Total loans	$ 2,823		$ 3,121