Loans and Allowance for Credit Losses - Activity in Allowance for Credit Losses by Portfolio Class (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	$ 6,960	$ 6,590	$ 8,010	$ 4,491
Change in accounting principle				1,499
Provision for credit losses	(170)	1,737	(997)	2,730
Loans charged-off	314	522	688	1,013
Less recoveries of loans charged-off	(134)	(85)	(285)	(183)
Net loan charge-offs (recoveries)	180	437	403	830
Balance at end of period	6,610	7,890	6,610	7,890
Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	1,932	2,240	2,423	1,484
Change in accounting principle				378
Provision for credit losses	(67)	516	(502)	968
Loans charged-off	58	125	144	213
Less recoveries of loans charged-off	(31)	(14)	(61)	(28)
Net loan charge-offs (recoveries)	27	111	83	185
Balance at end of period	1,838	2,645	1,838	2,645
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	1,532	841	1,544	799
Change in accounting principle				(122)
Provision for credit losses	(123)	450	(142)	612
Loans charged-off	4	23	14	23
Less recoveries of loans charged-off	(4)	(1)	(21)	(3)
Net loan charge-offs (recoveries)		22	(7)	20
Balance at end of period	1,409	1,269	1,409	1,269
Residential Mortgages [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	539	412	573	433
Change in accounting principle				(30)
Provision for credit losses	(71)	218	(110)	228
Loans charged-off	5	3	10	11
Less recoveries of loans charged-off	(15)	(6)	(25)	(13)
Net loan charge-offs (recoveries)	(10)	(3)	(15)	(2)
Balance at end of period	478	633	478	633
Other Retail [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	1,005	1,085	1,115	647
Change in accounting principle				401
Provision for credit losses	4	180	(71)	303
Loans charged-off	55	106	138	227
Less recoveries of loans charged-off	(40)	(28)	(88)	(63)
Net loan charge-offs (recoveries)	15	78	50	164
Balance at end of period	994	1,187	994	1,187
Credit Card [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	1,952	2,012	2,355	1,128
Change in accounting principle				872
Provision for credit losses	87	373	(172)	619
Loans charged-off	192	265	382	539
Less recoveries of loans charged-off	(44)	(36)	(90)	(76)
Net loan charge-offs (recoveries)	148	229	292	463
Balance at end of period	$ 1,891	$ 2,156	$ 1,891	$ 2,156