Loans and Allowance for Credit Losses - Summary of Loans by Portfolio Class and Company's Internal Credit Quality Rating (Detail) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 318,305	$ 296,102
Total outstanding commitments	635,813	624,548
Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	308,929	292,204
Total outstanding commitments	623,649	619,224
Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	6,443	1,643
Total outstanding commitments	8,604	2,451
Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,933	2,255
Total outstanding commitments	3,560	2,873
Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	9,376	3,898
Total outstanding commitments	12,164	5,324
Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	13,715	0
Originated in 2019	36,444	33,946
Originated in 2018	25,203	21,950
Originated in 2017	11,493	10,726
Originated in 2016	5,358	5,031
Originated prior to 2016	5,018	5,333
Revolving	29,086	26,877
Total loans	126,317	103,863
Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	13,238	0
Originated in 2019	35,323	33,550
Originated in 2018	23,843	21,394
Originated in 2017	10,983	10,464
Originated in 2016	5,236	4,984
Originated prior to 2016	4,745	5,151
Revolving	27,904	26,307
Total loans	121,272	101,850
Commercial [Member] | Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	392	0
Originated in 2019	846	174
Originated in 2018	991	420
Originated in 2017	318	165
Originated in 2016	85	10
Originated prior to 2016	148	86
Revolving	911	292
Total loans	3,691	1,147
Commercial [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	85	0
Originated in 2019	275	222
Originated in 2018	369	136
Originated in 2017	192	97
Originated in 2016	37	37
Originated prior to 2016	125	96
Revolving	271	278
Total loans	1,354	866
Commercial [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	477	0
Originated in 2019	1,121	396
Originated in 2018	1,360	556
Originated in 2017	510	262
Originated in 2016	122	47
Originated prior to 2016	273	182
Revolving	1,182	570
Total loans	5,045	2,013
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	3,183	0
Originated in 2019	12,971	13,192
Originated in 2018	9,172	9,582
Originated in 2017	5,387	6,026
Originated in 2016	3,531	3,883
Originated prior to 2016	4,637	5,086
Revolving	2,099	1,977
Total loans	40,980	39,746
Commercial Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	2,824	0
Originated in 2019	12,058	12,976
Originated in 2018	8,367	9,455
Originated in 2017	4,721	5,863
Originated in 2016	3,242	3,706
Originated prior to 2016	4,314	4,907
Revolving	2,072	1,965
Total loans	37,598	38,872
Commercial Real Estate [Member] | Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	339	0
Originated in 2019	705	108
Originated in 2018	705	71
Originated in 2017	568	99
Originated in 2016	215	117
Originated prior to 2016	189	78
Revolving	23	11
Total loans	2,744	484
Commercial Real Estate [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	20	0
Originated in 2019	208	108
Originated in 2018	100	56
Originated in 2017	98	64
Originated in 2016	74	60
Originated prior to 2016	134	101
Revolving	4	1
Total loans	638	390
Commercial Real Estate [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	359	0
Originated in 2019	913	216
Originated in 2018	805	127
Originated in 2017	666	163
Originated in 2016	289	177
Originated prior to 2016	323	179
Revolving	27	12
Total loans	3,382	874
Residential Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	5,108	0
Originated in 2019	17,912	18,822
Originated in 2018	8,222	9,215
Originated in 2017	8,978	9,626
Originated in 2016	10,808	11,407
Originated prior to 2016	20,147	21,516
Total loans	71,175	70,586
Residential Mortgages [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	5,108	0
Originated in 2019	17,909	18,819
Originated in 2018	8,211	9,204
Originated in 2017	8,961	9,605
Originated in 2016	10,779	11,378
Originated prior to 2016	19,821	21,168
Total loans	70,789	70,174
Residential Mortgages [Member] | Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	0	0
Originated in 2019	0	2
Originated in 2018	0	0
Originated in 2017	0	0
Originated in 2016	0	0
Originated prior to 2016	0	0
Total loans	0	2
Residential Mortgages [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	0	0
Originated in 2019	3	1
Originated in 2018	11	11
Originated in 2017	17	21
Originated in 2016	29	29
Originated prior to 2016	326	348
Total loans	386	410
Residential Mortgages [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	0	0
Originated in 2019	3	3
Originated in 2018	11	11
Originated in 2017	17	21
Originated in 2016	29	29
Originated prior to 2016	326	348
Total loans	386	412
Other Retail [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	4,173	0
Originated in 2019	14,761	15,918
Originated in 2018	9,332	10,154
Originated in 2017	6,862	7,935
Originated in 2016	3,112	3,699
Originated prior to 2016	2,888	3,302
Revolving	15,469	15,657
Revolving converted to term	455	453
Total loans	57,052	57,118
Other Retail [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	4,172	0
Originated in 2019	14,747	15,907
Originated in 2018	9,308	10,131
Originated in 2017	6,836	7,907
Originated in 2016	3,096	3,679
Originated prior to 2016	2,866	3,274
Revolving	15,336	15,509
Revolving converted to term	442	418
Total loans	56,783	56,825
Other Retail [Member] | Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	0	0
Originated in 2019	0	0
Originated in 2018	0	0
Originated in 2017	0	0
Originated in 2016	0	0
Originated prior to 2016	0	0
Revolving	8	10
Revolving converted to term	0	0
Total loans	8	10
Other Retail [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	1	0
Originated in 2019	14	11
Originated in 2018	24	23
Originated in 2017	26	28
Originated in 2016	16	20
Originated prior to 2016	22	28
Revolving	125	138
Revolving converted to term	33	35
Total loans	261	283
Other Retail [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	1	0
Originated in 2019	14	11
Originated in 2018	24	23
Originated in 2017	26	28
Originated in 2016	16	20
Originated prior to 2016	22	28
Revolving	133	148
Revolving converted to term	33	35
Total loans	269	293
Credit Card [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	22,781	24,789
Credit Card [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	22,487	24,483
Credit Card [Member] | Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Credit Card [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	294	306
Credit Card [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 294	$ 306