Loans and Allowance for Credit Losses - Summary of Loans by Portfolio Class and Company's Internal Credit Quality Rating (Detail) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 297,608	$ 297,707
Total outstanding commitments	656,903	645,752
Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	291,033	285,957
Total outstanding commitments	645,955	627,606
Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,318	4,278
Total outstanding commitments	4,606	8,772
Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,257	7,472
Total outstanding commitments	6,342	9,374
Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	6,575	11,750
Total outstanding commitments	10,948	18,146
Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2021	33,449
Originated in 2020	18,091	37,645
Originated in 2019	12,112	18,485
Originated in 2018	6,981	12,876
Originated in 2017	3,280	5,644
Originated prior to 2017	3,443	5,197
Revolving	23,657	23,024
Total loans	101,013	102,871
Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2021	32,826
Originated in 2020	17,202	34,557
Originated in 2019	11,851	17,867
Originated in 2018	6,853	12,349
Originated in 2017	3,213	5,257
Originated prior to 2017	3,373	4,954
Revolving	23,204	22,445
Total loans	98,522	97,429
Commercial [Member] | Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2021	346
Originated in 2020	637	1,335
Originated in 2019	198	269
Originated in 2018	77	351
Originated in 2017	14	117
Originated prior to 2017	30	128
Revolving	353	299
Total loans	1,655	2,499
Commercial [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2021	277
Originated in 2020	252	1,753
Originated in 2019	63	349
Originated in 2018	51	176
Originated in 2017	53	270
Originated prior to 2017	40	115
Revolving	100	280
Total loans	836	2,943
Commercial [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2021	623
Originated in 2020	889	3,088
Originated in 2019	261	618
Originated in 2018	128	527
Originated in 2017	67	387
Originated prior to 2017	70	243
Revolving	453	579
Total loans	2,491	5,442
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2021	10,278
Originated in 2020	8,792	11,044
Originated in 2019	8,374	10,973
Originated in 2018	4,134	7,103
Originated in 2017	2,118	3,188
Originated prior to 2017	3,368	5,311
Revolving	1,744	1,692
Total loans	38,808	39,311
Commercial Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2021	9,456
Originated in 2020	8,238	9,446
Originated in 2019	7,382	9,514
Originated in 2018	3,662	6,053
Originated in 2017	1,943	2,650
Originated prior to 2017	3,239	4,762
Revolving	1,556	1,445
Total loans	35,476	33,870
Commercial Real Estate [Member] | Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2021	50
Originated in 2020	119	461
Originated in 2019	298	454
Originated in 2018	142	411
Originated in 2017	25	198
Originated prior to 2017	26	240
Revolving	1	9
Total loans	661	1,773
Commercial Real Estate [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2021	772
Originated in 2020	435	1,137
Originated in 2019	694	1,005
Originated in 2018	330	639
Originated in 2017	150	340
Originated prior to 2017	103	309
Revolving	187	238
Total loans	2,671	3,668
Commercial Real Estate [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2021	822
Originated in 2020	554	1,598
Originated in 2019	992	1,459
Originated in 2018	472	1,050
Originated in 2017	175	538
Originated prior to 2017	129	549
Revolving	188	247
Total loans	3,332	5,441
Residential Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2021	21,045
Originated in 2020	18,049	23,266
Originated in 2019	8,527	13,987
Originated in 2018	3,513	5,693
Originated in 2017	4,515	6,943
Originated prior to 2017	19,304	26,265
Revolving	1	1
Total loans	74,954	76,155
Residential Mortgages [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2021	21,045
Originated in 2020	18,043	23,262
Originated in 2019	8,508	13,969
Originated in 2018	3,492	5,670
Originated in 2017	4,494	6,918
Originated prior to 2017	19,002	25,921
Revolving	1	1
Total loans	74,585	75,741
Residential Mortgages [Member] | Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	1	1
Originated in 2019	1	1
Originated in 2018		1
Originated in 2017		1
Originated prior to 2017		2
Total loans	2	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	21	22
Originated in 2017	21	24
Originated prior to 2017	302	342
Total loans	367	408
Residential Mortgages [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	6	4
Originated in 2019	19	18
Originated in 2018	21	23
Originated in 2017	21	25
Originated prior to 2017	302	344
Total loans	369	414
Other Retail [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2021	17,251
Originated in 2020	13,326	17,596
Originated in 2019	8,316	11,628
Originated in 2018	4,348	6,841
Originated in 2017	2,141	3,901
Originated prior to 2017	2,275	3,760
Revolving	12,523	12,757
Revolving converted to term	516	541
Total loans	60,696	57,024
Other Retail [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2021	17,248
Originated in 2020	13,318	17,589
Originated in 2019	8,300	11,605
Originated in 2018	4,332	6,814
Originated in 2017	2,130	3,879
Originated prior to 2017	2,259	3,731
Revolving	12,400	12,647
Revolving converted to term	473	503
Total loans	60,460	56,768
Other Retail [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2021	3
Originated in 2020	8	7
Originated in 2019	16	23
Originated in 2018	16	27
Originated in 2017	11	22
Originated prior to 2017	16	29
Revolving	123	110
Revolving converted to term	43	38
Total loans	236	256
Other Retail [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2021	3
Originated in 2020	8	7
Originated in 2019	16	23
Originated in 2018	16	27
Originated in 2017	11	22
Originated prior to 2017	16	29
Revolving	123	110
Revolving converted to term	43	38
Total loans	236	256
Credit Card [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	22,137	22,346
Credit Card [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	21,990	22,149
Credit Card [Member] | Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	147	197
Credit Card [Member] | Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 147	$ 197