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, 2020	Dec. 31, 2019
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 306,985	$ 296,102
Total outstanding commitments	652,512	624,548
Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	294,506	292,204
Total outstanding commitments	635,980	619,224
Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	7,800	1,643
Total outstanding commitments	10,868	2,451
Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,679	2,255
Total outstanding commitments	5,664	2,873
Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	12,479	3,898
Total outstanding commitments	16,532	5,324
Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	37,510
Originated in 2019	21,615	33,946
Originated in 2018	14,706	21,950
Originated in 2017	6,760	10,726
Originated in 2016	2,859	5,031
Originated prior to 2016	3,364	5,333
Revolving	23,950	26,877
Total loans	110,764	103,863
Commercial [Member] \| Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	34,060
Originated in 2019	20,897	33,550
Originated in 2018	14,093	21,394
Originated in 2017	6,356	10,464
Originated in 2016	2,761	4,984
Originated prior to 2016	3,235	5,151
Revolving	22,906	26,307
Total loans	104,308	101,850
Commercial [Member] \| Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	2,211
Originated in 2019	469	174
Originated in 2018	453	420
Originated in 2017	182	165
Originated in 2016	52	10
Originated prior to 2016	61	86
Revolving	756	292
Total loans	4,184	1,147
Commercial [Member] \| Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	1,239
Originated in 2019	249	222
Originated in 2018	160	136
Originated in 2017	222	97
Originated in 2016	46	37
Originated prior to 2016	68	96
Revolving	288	278
Total loans	2,272	866
Commercial [Member] \| Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	3,450
Originated in 2019	718	396
Originated in 2018	613	556
Originated in 2017	404	262
Originated in 2016	98	47
Originated prior to 2016	129	182
Revolving	1,044	570
Total loans	6,456	2,013
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	8,579
Originated in 2019	11,852	13,192
Originated in 2018	7,964	9,582
Originated in 2017	3,847	6,026
Originated in 2016	2,745	3,883
Originated prior to 2016	3,578	5,086
Revolving	1,814	1,977
Revolving converted to term	1
Total loans	40,380	39,746
Commercial Real Estate [Member] \| Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	7,276
Originated in 2019	10,517	12,976
Originated in 2018	6,880	9,455
Originated in 2017	3,305	5,863
Originated in 2016	2,338	3,706
Originated prior to 2016	3,167	4,907
Revolving	1,712	1,965
Revolving converted to term	1
Total loans	35,196	38,872
Commercial Real Estate [Member] \| Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	921
Originated in 2019	1,022	108
Originated in 2018	728	71
Originated in 2017	370	99
Originated in 2016	224	117
Originated prior to 2016	248	78
Revolving	97	11
Total loans	3,610	484
Commercial Real Estate [Member] \| Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	382
Originated in 2019	313	108
Originated in 2018	356	56
Originated in 2017	172	64
Originated in 2016	183	60
Originated prior to 2016	163	101
Revolving	5	1
Total loans	1,574	390
Commercial Real Estate [Member] \| Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	1,303
Originated in 2019	1,335	216
Originated in 2018	1,084	127
Originated in 2017	542	163
Originated in 2016	407	177
Originated prior to 2016	411	179
Revolving	102	12
Total loans	5,184	874
Residential Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	18,804
Originated in 2019	15,325	18,822
Originated in 2018	6,489	9,215
Originated in 2017	7,763	9,626
Originated in 2016	9,499	11,407
Originated prior to 2016	18,908	21,516
Revolving	1
Total loans	76,789	70,586
Residential Mortgages [Member] \| Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	18,800
Originated in 2019	15,313	18,819
Originated in 2018	6,468	9,204
Originated in 2017	7,745	9,605
Originated in 2016	9,469	11,378
Originated prior to 2016	18,597	21,168
Revolving	1
Total loans	76,393	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
Total loans	6	2
Residential Mortgages [Member] \| Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	3
Originated in 2019	9	1
Originated in 2018	20	11
Originated in 2017	17	21
Originated in 2016	30	29
Originated prior to 2016	311	348
Total loans	390	410
Residential Mortgages [Member] \| Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	4
Originated in 2019	12	3
Originated in 2018	21	11
Originated in 2017	18	21
Originated in 2016	30	29
Originated prior to 2016	311	348
Total loans	396	412
Other Retail [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	13,419
Originated in 2019	12,543	15,918
Originated in 2018	7,597	10,154
Originated in 2017	4,730	7,935
Originated in 2016	2,174	3,699
Originated prior to 2016	2,152	3,302
Revolving	14,055	15,657
Revolving converted to term	484	453
Total loans	57,154	57,118
Other Retail [Member] \| Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	13,416
Originated in 2019	12,527	15,907
Originated in 2018	7,574	10,131
Originated in 2017	4,708	7,907
Originated in 2016	2,162	3,679
Originated prior to 2016	2,135	3,274
Revolving	13,939	15,509
Revolving converted to term	449	418
Total loans	56,910	56,825
Other Retail [Member] \| Special Mention Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Revolving		10
Total loans		10
Other Retail [Member] \| Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	3
Originated in 2019	16	11
Originated in 2018	23	23
Originated in 2017	22	28
Originated in 2016	12	20
Originated prior to 2016	17	28
Revolving	116	138
Revolving converted to term	35	35
Total loans	244	283
Other Retail [Member] \| Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Originated in 2020	3
Originated in 2019	16	11
Originated in 2018	23	23
Originated in 2017	22	28
Originated in 2016	12	20
Originated prior to 2016	17	28
Revolving	116	148
Revolving converted to term	35	35
Total loans	244	293
Credit Card [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	21,898	24,789
Credit Card [Member] \| Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	21,699	24,483
Credit Card [Member] \| Classified Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	199	306
Credit Card [Member] \| Total Criticized [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 199	$ 306

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