Loans and Allowance for Credit Losses - Activity in Allowance for Credit Losses by Portfolio Class (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	$ 7,890	$ 4,466	$ 4,491	$ 4,441
Change in accounting principle			1,499
Provision for credit losses	635	367	3,365	1,109
Loans charged-off	611	451	1,624	1,388
Less recoveries of loans charged-off	(96)	(99)	(279)	(319)
Net loans charged-off	515	352	1,345	1,069
Balance at end of period	8,010	4,481	8,010	4,481
Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	2,645	1,464	1,484	1,454
Change in accounting principle			378
Provision for credit losses	20	101	988	243
Loans charged-off	193	91	406	300
Less recoveries of loans charged-off	(15)	(16)	(43)	(93)
Net loans charged-off	178	75	363	207
Balance at end of period	2,487	1,490	2,487	1,490
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	1,269	794	799	800
Change in accounting principle			(122)
Provision for credit losses	263	3	875	(2)
Loans charged-off	89	7	112	11
Less recoveries of loans charged-off	(6)	(1)	(9)	(4)
Net loans charged-off	83	6	103	7
Balance at end of period	1,449	791	1,449	791
Residential Mortgages [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	633	438	433	455
Change in accounting principle			(30)
Provision for credit losses	(49)	(10)	179	(20)
Loans charged-off	4	8	15	27
Less recoveries of loans charged-off	(7)	(11)	(20)	(23)
Net loans charged-off	(3)	(3)	(5)	4
Balance at end of period	587	431	587	431
Other Retail [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	1,187	638	647	630
Change in accounting principle			401
Provision for credit losses	32	61	335	194
Loans charged-off	89	97	316	283
Less recoveries of loans charged-off	(33)	(34)	(96)	(95)
Net loans charged-off	56	63	220	188
Balance at end of period	1,163	636	1,163	636
Credit Card [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	2,156	1,132	1,128	1,102
Change in accounting principle			872
Provision for credit losses	369	212	988	694
Loans charged-off	236	248	775	767
Less recoveries of loans charged-off	(35)	(37)	(111)	(104)
Net loans charged-off	201	211	664	663
Balance at end of period	$ 2,324	$ 1,133	$ 2,324	$ 1,133