Allowance for Loan and Lease Losses - Summary of Changes in Allowance for Loan and Lease Losses (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period	$ 7,220
Balance at end of the period	7,313
Provision for credit losses	1,693	$ 1,674
Allowance
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period	7,220	7,502
Charge-offs	(2,273)	(2,276)
Recoveries	674	658
Net charge-offs	(1,599)	(1,618)
Provision (benefit) for loan and lease losses	1,684	1,684
Allowance build (release) for loan and lease losses	85	66
Other changes	8	(1)
Balance at end of the period	7,313	7,567
Reserve for unfunded lending commitments
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period	122	124
Provision (benefit) for loan and lease losses	9	(10)
Balance at end of the period	131	114
Combined allowance and reserve
Allowance for Loan and Lease Losses [Roll Forward]
Balance at end of the period	7,444	7,681
Credit Card
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period	5,535	5,648
Charge-offs	(1,782)	(1,825)
Recoveries	418	448
Net charge-offs	(1,364)	(1,377)
Provision (benefit) for loan and lease losses	1,389	1,456
Allowance build (release) for loan and lease losses	25	79
Other changes	8	(1)
Balance at end of the period	5,568	5,726
Credit Card | Reserve for unfunded lending commitments
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period	0	0
Provision (benefit) for loan and lease losses	0	0
Balance at end of the period	0	0
Credit Card | Combined allowance and reserve
Allowance for Loan and Lease Losses [Roll Forward]
Balance at end of the period	5,568	5,726
Consumer Banking
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period	1,048	1,242
Charge-offs	(471)	(431)
Recoveries	250	208
Net charge-offs	(221)	(223)
Provision (benefit) for loan and lease losses	235	234
Allowance build (release) for loan and lease losses	14	11
Other changes	0	0
Balance at end of the period	1,062	1,253
Consumer Banking | Reserve for unfunded lending commitments
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period	4	7
Provision (benefit) for loan and lease losses	0	(1)
Balance at end of the period	4	6
Consumer Banking | Combined allowance and reserve
Allowance for Loan and Lease Losses [Roll Forward]
Balance at end of the period	1,066	1,259
Consumer Banking | Home loan
Allowance for Loan and Lease Losses [Roll Forward]
Net charge-offs	0	1
Commercial Banking
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period	637	611
Charge-offs	(20)	(21)
Recoveries	6	2
Net charge-offs	(14)	(19)
Provision (benefit) for loan and lease losses	60	(5)
Allowance build (release) for loan and lease losses	46	(24)
Other changes	0	0
Balance at end of the period	683	587
Commercial Banking | Reserve for unfunded lending commitments
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period	118	117
Provision (benefit) for loan and lease losses	9	(9)
Balance at end of the period	127	108
Commercial Banking | Combined allowance and reserve
Allowance for Loan and Lease Losses [Roll Forward]
Balance at end of the period	810	695
Other
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period		1
Charge-offs		1
Recoveries		0
Net charge-offs		1
Provision (benefit) for loan and lease losses		(1)
Allowance build (release) for loan and lease losses		0
Other changes		0
Balance at end of the period		1
Other | Reserve for unfunded lending commitments
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period		0
Provision (benefit) for loan and lease losses		0
Balance at end of the period		0
Other | Combined allowance and reserve
Allowance for Loan and Lease Losses [Roll Forward]
Balance at end of the period		1
Other
Allowance for Loan and Lease Losses [Roll Forward]
Provision for credit losses	$ 0	$ (1)