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, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	$ 6,590	$ 4,451	$ 4,491	$ 4,441
Change in accounting principle			1,499
Provision for credit losses	1,737	365	2,730	742
Loans charged-off	522	464	1,013	937
Less recoveries of loans charged-off	(85)	(114)	(183)	(220)
Net loans charged-off	437	350	830	717
Balance at end of period	7,890	4,466	7,890	4,466
Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	2,240	1,445	1,484	1,454
Change in accounting principle			378
Provision for credit losses	516	78	968	142
Loans charged-off	125	98	213	209
Less recoveries of loans charged-off	(14)	(39)	(28)	(77)
Net loans charged-off	111	59	185	132
Balance at end of period	2,645	1,464	2,645	1,464
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	841	812	799	800
Change in accounting principle			(122)
Provision for credit losses	450	(17)	612	(5)
Loans charged-off	23	3	23	4
Less recoveries of loans charged-off	(1)	(2)	(3)	(3)
Net loans charged-off	22	1	20	1
Balance at end of period	1,269	794	1,269	794
Residential Mortgages [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	412	445	433	455
Change in accounting principle			(30)
Provision for credit losses	218	(3)	228	(10)
Loans charged-off	3	11	11	19
Less recoveries of loans charged-off	(6)	(7)	(13)	(12)
Net loans charged-off	(3)	4	(2)	7
Balance at end of period	633	438	633	438
Other Retail [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	1,085	634	647	630
Change in accounting principle			401
Provision for credit losses	180	63	303	133
Loans charged-off	106	90	227	186
Less recoveries of loans charged-off	(28)	(31)	(63)	(61)
Net loans charged-off	78	59	164	125
Balance at end of period	1,187	638	1,187	638
Credit Card [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	2,012	1,115	1,128	1,102
Change in accounting principle			872
Provision for credit losses	373	244	619	482
Loans charged-off	265	262	539	519
Less recoveries of loans charged-off	(36)	(35)	(76)	(67)
Net loans charged-off	229	227	463	452
Balance at end of period	$ 2,156	$ 1,132	$ 2,156	$ 1,132