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, 2021	Dec. 31, 2020
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 296,912	$ 297,707
Total outstanding commitments	650,228	645,752
Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	288,745	285,957
Total outstanding commitments	636,535	627,606
Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,151	4,278
Total outstanding commitments	6,624	8,772
Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	5,016	7,472
Total outstanding commitments	7,069	9,374
Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	8,167	11,750
Total outstanding commitments	13,693	18,146
Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2021	24,632
Originated in 2020	23,743	37,645
Originated in 2019	13,979	18,485
Originated in 2018	9,454	12,876
Originated in 2017	3,951	5,644
Originated prior to 2017	3,678	5,197
Revolving	24,084	23,024
Total loans	103,521	102,871
Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2021	23,974
Originated in 2020	22,215	34,557
Originated in 2019	13,662	17,867
Originated in 2018	9,217	12,349
Originated in 2017	3,874	5,257
Originated prior to 2017	3,544	4,954
Revolving	23,809	22,445
Total loans	100,295	97,429
Commercial [Member] | Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2021	453
Originated in 2020	981	1,335
Originated in 2019	245	269
Originated in 2018	145	351
Originated in 2017	14	117
Originated prior to 2017	78	128
Revolving	90	299
Total loans	2,006	2,499
Commercial [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2021	205
Originated in 2020	547	1,753
Originated in 2019	72	349
Originated in 2018	92	176
Originated in 2017	63	270
Originated prior to 2017	56	115
Revolving	185	280
Total loans	1,220	2,943
Commercial [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2021	658
Originated in 2020	1,528	3,088
Originated in 2019	317	618
Originated in 2018	237	527
Originated in 2017	77	387
Originated prior to 2017	134	243
Revolving	275	579
Total loans	3,226	5,442
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2021	6,678
Originated in 2020	9,616	11,044
Originated in 2019	9,382	10,973
Originated in 2018	4,917	7,103
Originated in 2017	2,498	3,188
Originated prior to 2017	3,953	5,311
Revolving	1,726	1,692
Total loans	38,770	39,311
Commercial Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2021	5,911
Originated in 2020	8,917	9,446
Originated in 2019	8,148	9,514
Originated in 2018	4,211	6,053
Originated in 2017	2,150	2,650
Originated prior to 2017	3,763	4,762
Revolving	1,515	1,445
Total loans	34,615	33,870
Commercial Real Estate [Member] | Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2021	74
Originated in 2020	167	461
Originated in 2019	444	454
Originated in 2018	275	411
Originated in 2017	94	198
Originated prior to 2017	80	240
Revolving	6	9
Total loans	1,140	1,773
Commercial Real Estate [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2021	693
Originated in 2020	532	1,137
Originated in 2019	790	1,005
Originated in 2018	431	639
Originated in 2017	254	340
Originated prior to 2017	110	309
Revolving	205	238
Total loans	3,015	3,668
Commercial Real Estate [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2021	767
Originated in 2020	699	1,598
Originated in 2019	1,234	1,459
Originated in 2018	706	1,050
Originated in 2017	348	538
Originated prior to 2017	190	549
Revolving	211	247
Total loans	4,155	5,441
Residential Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2021	11,717
Originated in 2020	20,417	23,266
Originated in 2019	10,192	13,987
Originated in 2018	4,172	5,693
Originated in 2017	5,243	6,943
Originated prior to 2017	21,624	26,265
Revolving	1	1
Total loans	73,366	76,155
Residential Mortgages [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2021	11,717
Originated in 2020	20,412	23,262
Originated in 2019	10,173	13,969
Originated in 2018	4,149	5,670
Originated in 2017	5,224	6,918
Originated prior to 2017	21,305	25,921
Revolving	1	1
Total loans	72,981	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
Originated prior to 2017	3	2
Total loans	5	6
Residential Mortgages [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	5	3
Originated in 2019	18	17
Originated in 2018	22	22
Originated in 2017	19	24
Originated prior to 2017	316	342
Total loans	380	408
Residential Mortgages [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	5	4
Originated in 2019	19	18
Originated in 2018	23	23
Originated in 2017	19	25
Originated prior to 2017	319	344
Total loans	385	414
Other Retail [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2021	12,437
Originated in 2020	14,512	17,596
Originated in 2019	9,179	11,628
Originated in 2018	4,862	6,841
Originated in 2017	2,521	3,901
Originated prior to 2017	2,649	3,760
Revolving	12,749	12,757
Revolving converted to term	530	541
Total loans	59,439	57,024
Other Retail [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2021	12,435
Originated in 2020	14,505	17,589
Originated in 2019	9,163	11,605
Originated in 2018	4,844	6,814
Originated in 2017	2,509	3,879
Originated prior to 2017	2,632	3,731
Revolving	12,618	12,647
Revolving converted to term	485	503
Total loans	59,191	56,768
Other Retail [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2021	2
Originated in 2020	7	7
Originated in 2019	16	23
Originated in 2018	18	27
Originated in 2017	12	22
Originated prior to 2017	17	29
Revolving	131	110
Revolving converted to term	45	38
Total loans	248	256
Other Retail [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2021	2
Originated in 2020	7	7
Originated in 2019	16	23
Originated in 2018	18	27
Originated in 2017	12	22
Originated prior to 2017	17	29
Revolving	131	110
Revolving converted to term	45	38
Total loans	248	256
Credit Card [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	21,816	22,346
Credit Card [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	21,663	22,149
Credit Card [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	153	197
Credit Card [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 153	$ 197