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, 2019	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Allowance Balance at End of Period
Loans individually evaluated for impairment	$ 18		$ 24
TDRs collectively evaluated for impairment	223		225
Other loans collectively evaluated for impairment	4,210		4,176
Loans acquired with deteriorated credit quality	15		16
Total allowance for credit losses	4,466	$ 4,451	4,441	$ 4,411	$ 4,417	$ 4,417
Loan Balance at End of Period
Loans individually evaluated for impairment	338		348
TDRs collectively evaluated for impairment	3,853		3,960
Other loans collectively evaluated for impairment	287,524		282,158
Loans acquired with deteriorated credit quality	313		344
Total loans	292,028		286,810
Commercial [Member]
Allowance Balance at End of Period
Loans individually evaluated for impairment	16		16
TDRs collectively evaluated for impairment	19		15
Other loans collectively evaluated for impairment	1,429		1,423
Total allowance for credit losses	1,464	1,445	1,454	1,391	1,386	1,372
Loan Balance at End of Period
Loans individually evaluated for impairment	298		262
TDRs collectively evaluated for impairment	157		151
Other loans collectively evaluated for impairment	103,525		102,031
Total loans	103,980		102,444
Commercial Real Estate [Member]
Allowance Balance at End of Period
Loans individually evaluated for impairment	2		8
TDRs collectively evaluated for impairment	5		3
Other loans collectively evaluated for impairment	787		788
Loans acquired with deteriorated credit quality			1
Total allowance for credit losses	794	812	800	812	826	831
Loan Balance at End of Period
Loans individually evaluated for impairment	40		86
TDRs collectively evaluated for impairment	127		129
Other loans collectively evaluated for impairment	39,131		39,297
Loans acquired with deteriorated credit quality	36		27
Total loans	39,334		39,539
Residential Mortgages [Member]
Allowance Balance at End of Period
TDRs collectively evaluated for impairment	109		126
Other loans collectively evaluated for impairment	314		314
Loans acquired with deteriorated credit quality	15		15
Total allowance for credit losses	438	445	455	436	443	449
Loan Balance at End of Period
TDRs collectively evaluated for impairment	3,125		3,252
Other loans collectively evaluated for impairment	64,511		61,465
Loans acquired with deteriorated credit quality	277		317
Total loans	67,913		65,034
Other Retail [Member]
Allowance Balance at End of Period
TDRs collectively evaluated for impairment	12		12
Other loans collectively evaluated for impairment	626		618
Total allowance for credit losses	638	634	630	667	672	678
Loan Balance at End of Period
TDRs collectively evaluated for impairment	186		183
Other loans collectively evaluated for impairment	57,189		56,247
Total loans	57,375		56,430
Credit Card [Member]
Allowance Balance at End of Period
TDRs collectively evaluated for impairment	78		69
Other loans collectively evaluated for impairment	1,054		1,033
Total allowance for credit losses	1,132	$ 1,115	1,102	$ 1,082	$ 1,064	$ 1,056
Loan Balance at End of Period
TDRs collectively evaluated for impairment	258		245
Other loans collectively evaluated for impairment	23,168		23,118
Total loans	$ 23,426		$ 23,363