Loans and Allowance for Credit Losses - Activity in Allowance for Credit Losses by Portfolio Class (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	$ 4,491	$ 4,441
Change in accounting principle	1,499
Provision for credit losses	993	377
Loans charged-off	491	473
Less recoveries of loans charged-off	(98)	(106)
Net loans charged-off	393	367
Balance at end of period	6,590	4,451
Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	1,484	1,454
Change in accounting principle	378
Provision for credit losses	452	64
Loans charged-off	88	111
Less recoveries of loans charged-off	(14)	(38)
Net loans charged-off	74	73
Balance at end of period	2,240	1,445
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	799	800
Change in accounting principle	(122)
Provision for credit losses	162	12
Loans charged-off		1
Less recoveries of loans charged-off	(2)	(1)
Net loans charged-off	(2)
Balance at end of period	841	812
Residential Mortgages [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	433	455
Change in accounting principle	(30)
Provision for credit losses	10	(7)
Loans charged-off	8	8
Less recoveries of loans charged-off	(7)	(5)
Net loans charged-off	1	3
Balance at end of period	412	445
Other Retail [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	647	630
Change in accounting principle	401
Provision for credit losses	123	70
Loans charged-off	121	96
Less recoveries of loans charged-off	(35)	(30)
Net loans charged-off	86	66
Balance at end of period	1,085	634
Credit Card [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	1,128	1,102
Change in accounting principle	872
Provision for credit losses	246	238
Loans charged-off	274	257
Less recoveries of loans charged-off	(40)	(32)
Net loans charged-off	234	225
Balance at end of period	$ 2,012	$ 1,115