Loans and Allowance for Credit Losses - Summary of Loans by Portfolio Class and Company's Internal Credit Quality Rating (Detail) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 310,335	$ 296,102
Total outstanding commitments	646,133	624,548
Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	298,310	292,204
Total outstanding commitments	630,092	619,224
Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	7,594	1,643
Total outstanding commitments	10,740	2,451
Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,431	2,255
Total outstanding commitments	5,301	2,873
Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	12,025	3,898
Total outstanding commitments	16,041	5,324
Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	33,800
Originated in 2019	25,817	33,946
Originated in 2018	18,261	21,950
Originated in 2017	8,453	10,726
Originated in 2016	3,997	5,031
Originated prior to 2016	4,325	5,333
Revolving	25,608	26,877
Total loans	120,261	103,863
Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	31,789
Originated in 2019	24,882	33,550
Originated in 2018	17,201	21,394
Originated in 2017	8,020	10,464
Originated in 2016	3,674	4,984
Originated prior to 2016	4,004	5,151
Revolving	24,470	26,307
Total loans	114,040	101,850
Commercial [Member] | Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	1,360
Originated in 2019	603	174
Originated in 2018	684	420
Originated in 2017	177	165
Originated in 2016	266	10
Originated prior to 2016	53	86
Revolving	678	292
Total loans	3,821	1,147
Commercial [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	651
Originated in 2019	332	222
Originated in 2018	376	136
Originated in 2017	256	97
Originated in 2016	57	37
Originated prior to 2016	268	96
Revolving	460	278
Total loans	2,400	866
Commercial [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	2,011
Originated in 2019	935	396
Originated in 2018	1,060	556
Originated in 2017	433	262
Originated in 2016	323	47
Originated prior to 2016	321	182
Revolving	1,138	570
Total loans	6,221	2,013
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	6,749
Originated in 2019	12,255	13,192
Originated in 2018	8,522	9,582
Originated in 2017	4,413	6,026
Originated in 2016	3,016	3,883
Originated prior to 2016	4,112	5,086
Revolving	2,009	1,977
Total loans	41,076	39,746
Commercial Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	5,903
Originated in 2019	10,813	12,976
Originated in 2018	7,470	9,455
Originated in 2017	3,773	5,863
Originated in 2016	2,644	3,706
Originated prior to 2016	3,692	4,907
Revolving	1,900	1,965
Total loans	36,195	38,872
Commercial Real Estate [Member] | Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	706
Originated in 2019	1,214	108
Originated in 2018	826	71
Originated in 2017	409	99
Originated in 2016	243	117
Originated prior to 2016	267	78
Revolving	102	11
Total loans	3,767	484
Commercial Real Estate [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	140
Originated in 2019	228	108
Originated in 2018	226	56
Originated in 2017	231	64
Originated in 2016	129	60
Originated prior to 2016	153	101
Revolving	7	1
Total loans	1,114	390
Commercial Real Estate [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	846
Originated in 2019	1,442	216
Originated in 2018	1,052	127
Originated in 2017	640	163
Originated in 2016	372	177
Originated prior to 2016	420	179
Revolving	109	12
Total loans	4,881	874
Residential Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	11,998
Originated in 2019	15,929	18,822
Originated in 2018	6,975	9,215
Originated in 2017	8,016	9,626
Originated in 2016	9,899	11,407
Originated prior to 2016	18,511	21,516
Revolving	1
Total loans	71,329	70,586
Residential Mortgages [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	11,996
Originated in 2019	15,921	18,819
Originated in 2018	6,955	9,204
Originated in 2017	7,993	9,605
Originated in 2016	9,868	11,378
Originated prior to 2016	18,192	21,168
Revolving	1
Total loans	70,926	70,174
Residential Mortgages [Member] | Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	1
Originated in 2019	3	2
Originated in 2018	1
Originated in 2017	1
Originated in 2016
Originated prior to 2016
Revolving
Total loans	6	2
Residential Mortgages [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	1
Originated in 2019	5	1
Originated in 2018	19	11
Originated in 2017	22	21
Originated in 2016	31	29
Originated prior to 2016	319	348
Revolving
Total loans	397	410
Residential Mortgages [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	2
Originated in 2019	8	3
Originated in 2018	20	11
Originated in 2017	23	21
Originated in 2016	31	29
Originated prior to 2016	319	348
Revolving
Total loans	403	412
Other Retail [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	8,268
Originated in 2019	13,670	15,918
Originated in 2018	8,478	10,154
Originated in 2017	5,836	7,935
Originated in 2016	2,627	3,699
Originated prior to 2016	2,501	3,302
Revolving	14,562	15,657
Revolving converted to term	470	453
Total loans	56,412	57,118
Other Retail [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	8,265
Originated in 2019	13,648	15,907
Originated in 2018	8,449	10,131
Originated in 2017	5,809	7,907
Originated in 2016	2,611	3,679
Originated prior to 2016	2,481	3,274
Revolving	14,450	15,509
Revolving converted to term	438	418
Total loans	56,151	56,825
Other Retail [Member] | Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020
Originated in 2019
Originated in 2018
Originated in 2017
Originated in 2016
Originated prior to 2016
Revolving		10
Revolving converted to term
Total loans		10
Other Retail [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	3
Originated in 2019	22	11
Originated in 2018	29	23
Originated in 2017	27	28
Originated in 2016	16	20
Originated prior to 2016	20	28
Revolving	112	138
Revolving converted to term	32	35
Total loans	261	283
Other Retail [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	3
Originated in 2019	22	11
Originated in 2018	29	23
Originated in 2017	27	28
Originated in 2016	16	20
Originated prior to 2016	20	28
Revolving	112	148
Revolving converted to term	32	35
Total loans	261	293
Credit Card [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	21,257	24,789
Credit Card [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	20,998	24,483
Credit Card [Member] | Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans
Credit Card [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	259	306
Credit Card [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 259	$ 306