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, 2021	Dec. 31, 2020
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 294,427	$ 297,707
Total outstanding commitments	646,659	645,752
Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	283,696	285,957
Total outstanding commitments	629,280	627,606
Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,995	4,278
Total outstanding commitments	8,140	8,772
Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	6,736	7,472
Total outstanding commitments	9,239	9,374
Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	10,731	11,750
Total outstanding commitments	17,379	18,146
Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2021	13,135
Originated in 2020	31,195	37,645
Originated in 2019	16,284	18,485
Originated in 2018	11,432	12,876
Originated in 2017	4,920	5,644
Originated prior to 2017	4,374	5,197
Revolving	22,818	23,024
Total loans	104,158	102,871
Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2021	12,604
Originated in 2020	28,890	34,557
Originated in 2019	15,710	17,867
Originated in 2018	10,909	12,349
Originated in 2017	4,658	5,257
Originated prior to 2017	4,133	4,954
Revolving	22,377	22,445
Total loans	99,281	97,429
Commercial [Member] | Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2021	313
Originated in 2020	1,003	1,335
Originated in 2019	351	269
Originated in 2018	372	351
Originated in 2017	81	117
Originated prior to 2017	168	128
Revolving	206	299
Total loans	2,494	2,499
Commercial [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2021	218
Originated in 2020	1,302	1,753
Originated in 2019	223	349
Originated in 2018	151	176
Originated in 2017	181	270
Originated prior to 2017	73	115
Revolving	235	280
Total loans	2,383	2,943
Commercial [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2021	531
Originated in 2020	2,305	3,088
Originated in 2019	574	618
Originated in 2018	523	527
Originated in 2017	262	387
Originated prior to 2017	241	243
Revolving	441	579
Total loans	4,877	5,442
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2021	2,815
Originated in 2020	10,126	11,044
Originated in 2019	10,185	10,973
Originated in 2018	6,168	7,103
Originated in 2017	2,866	3,188
Originated prior to 2017	4,584	5,311
Revolving	1,688	1,692
Revolving converted to term	538
Total loans	38,432	39,311
Commercial Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2021	2,368
Originated in 2020	8,889	9,446
Originated in 2019	8,788	9,514
Originated in 2018	5,296	6,053
Originated in 2017	2,375	2,650
Originated prior to 2017	4,272	4,762
Revolving	1,457	1,445
Total loans	33,445	33,870
Commercial Real Estate [Member] | Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2021	39
Originated in 2020	336	461
Originated in 2019	450	454
Originated in 2018	373	411
Originated in 2017	141	198
Originated prior to 2017	151	240
Revolving	5	9
Total loans	1,495	1,773
Commercial Real Estate [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2021	408
Originated in 2020	901	1,137
Originated in 2019	947	1,005
Originated in 2018	499	639
Originated in 2017	350	340
Originated prior to 2017	161	309
Revolving	226	238
Total loans	3,492	3,668
Commercial Real Estate [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2021	447
Originated in 2020	1,237	1,598
Originated in 2019	1,397	1,459
Originated in 2018	872	1,050
Originated in 2017	491	538
Originated prior to 2017	312	549
Revolving	231	247
Total loans	4,987	5,441
Residential Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2021	4,208
Originated in 2020	22,058	23,266
Originated in 2019	12,108	13,987
Originated in 2018	5,015	5,693
Originated in 2017	6,114	6,943
Originated prior to 2017	24,120	26,265
Revolving	1	1
Total loans	73,624	76,155
Residential Mortgages [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2021	4,208
Originated in 2020	22,053	23,262
Originated in 2019	12,084	13,969
Originated in 2018	4,989	5,670
Originated in 2017	6,091	6,918
Originated prior to 2017	23,782	25,921
Revolving	1	1
Total loans	73,208	75,741
Residential Mortgages [Member] | Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020		1
Originated in 2019	1	1
Originated in 2018	1	1
Originated in 2017	1	1
Originated prior to 2017	3	2
Total loans	6	6
Residential Mortgages [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	5	3
Originated in 2019	23	17
Originated in 2018	25	22
Originated in 2017	22	24
Originated prior to 2017	335	342
Total loans	410	408
Residential Mortgages [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	5	4
Originated in 2019	24	18
Originated in 2018	26	23
Originated in 2017	23	25
Originated prior to 2017	338	344
Total loans	416	414
Other Retail [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2021	5,691
Originated in 2020	15,960	17,596
Originated in 2019	10,367	11,628
Originated in 2018	5,842	6,841
Originated in 2017	3,120	3,901
Originated prior to 2017	3,152	3,760
Revolving	12,671	12,757
Revolving converted to term		541
Total loans	57,341	57,024
Other Retail [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2021	5,690
Originated in 2020	15,954	17,589
Originated in 2019	10,351	11,605
Originated in 2018	5,822	6,814
Originated in 2017	3,106	3,879
Originated prior to 2017	3,134	3,731
Revolving	12,536	12,647
Revolving converted to term	495	503
Total loans	57,088	56,768
Other Retail [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2021	1
Originated in 2020	6	7
Originated in 2019	16	23
Originated in 2018	20	27
Originated in 2017	14	22
Originated prior to 2017	18	29
Revolving	135	110
Revolving converted to term	43	38
Total loans	253	256
Other Retail [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2021	1
Originated in 2020	6	7
Originated in 2019	16	23
Originated in 2018	20	27
Originated in 2017	14	22
Originated prior to 2017	18	29
Revolving	135	110
Revolving converted to term	43	38
Total loans	253	256
Credit Card [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	20,872	22,346
Credit Card [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	20,674	22,149
Credit Card [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	198	197
Credit Card [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 198	$ 197