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, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Allowance Balance at End of Period
Loans individually evaluated for impairment	$ 33	$ 24
TDRs collectively evaluated for impairment	225	225
Other loans collectively evaluated for impairment	4,178	4,176
Loans acquired with deteriorated credit quality	15	16
Total allowance for credit losses	4,451	4,441	$ 4,417	$ 4,417
Loan Balance at End of Period
Loans individually evaluated for impairment	360	348
TDRs collectively evaluated for impairment	3,905	3,960
Other loans collectively evaluated for impairment	283,103	282,158
Loans acquired with deteriorated credit quality	331	344
Total loans	287,699	286,810
Commercial [Member]
Allowance Balance at End of Period
Loans individually evaluated for impairment	31	16
TDRs collectively evaluated for impairment	18	15
Other loans collectively evaluated for impairment	1,396	1,423
Total allowance for credit losses	1,445	1,454	1,386	1,372
Loan Balance at End of Period
Loans individually evaluated for impairment	284	262
TDRs collectively evaluated for impairment	160	151
Other loans collectively evaluated for impairment	102,625	102,031
Total loans	103,069	102,444
Commercial Real Estate [Member]
Allowance Balance at End of Period
Loans individually evaluated for impairment	2	8
TDRs collectively evaluated for impairment	4	3
Other loans collectively evaluated for impairment	806	788
Loans acquired with deteriorated credit quality		1
Total allowance for credit losses	812	800	826	831
Loan Balance at End of Period
Loans individually evaluated for impairment	76	86
TDRs collectively evaluated for impairment	143	129
Other loans collectively evaluated for impairment	39,171	39,297
Loans acquired with deteriorated credit quality	31	27
Total loans	39,421	39,539
Residential Mortgages [Member]
Allowance Balance at End of Period
TDRs collectively evaluated for impairment	117	126
Other loans collectively evaluated for impairment	313	314
Loans acquired with deteriorated credit quality	15	15
Total allowance for credit losses	445	455	443	449
Loan Balance at End of Period
TDRs collectively evaluated for impairment	3,158	3,252
Other loans collectively evaluated for impairment	62,785	61,465
Loans acquired with deteriorated credit quality	300	317
Total loans	66,243	65,034
Other Retail [Member]
Allowance Balance at End of Period
TDRs collectively evaluated for impairment	12	12
Other loans collectively evaluated for impairment	622	618
Total allowance for credit losses	634	630	672	678
Loan Balance at End of Period
TDRs collectively evaluated for impairment	190	183
Other loans collectively evaluated for impairment	56,508	56,247
Total loans	56,698	56,430
Credit Card [Member]
Allowance Balance at End of Period
TDRs collectively evaluated for impairment	74	69
Other loans collectively evaluated for impairment	1,041	1,033
Total allowance for credit losses	1,115	1,102	$ 1,064	$ 1,056
Loan Balance at End of Period
TDRs collectively evaluated for impairment	254	245
Other loans collectively evaluated for impairment	22,014	23,118
Total loans	$ 22,268	$ 23,363