Allowance for Loan and Lease Losses - Summary of Changes in Allowance for Loan and Lease Losses (Detail) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Jun. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period				$ 7,220
Balance at end of the period	$ 7,037			7,037
Provision (benefit) for credit losses	1,383	$ 1,268		4,418	$ 4,218
Allowance
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period	7,133	7,368		7,220	7,502
Charge-offs	(2,086)	(2,044)		(6,516)	(6,429)
Recoveries	624	619		1,947	1,927
Net charge-offs	(1,462)	(1,425)		(4,569)	(4,502)
Provision (benefit) for loan and lease losses	1,374	1,275		4,387	4,232
Allowance build (release) for loan and lease losses	(88)	(150)		(182)	(270)
Other changes	(8)	1		(1)	(13)
Balance at end of the period	7,037	7,219	$ 7,368	7,037	7,219
Reserve for unfunded lending commitments
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period	144	117		122	124
Provision (benefit) for loan and lease losses	9	(7)		31	(14)
Balance at end of the period	153	110	117	153	110
Combined allowance and reserve
Allowance for Loan and Lease Losses [Roll Forward]
Balance at end of the period	7,190	7,329		7,190	7,329
Credit Card
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period	5,342	5,624		5,535	5,648
Charge-offs	(1,531)	(1,528)		(5,024)	(5,032)
Recoveries	380	391		1,189	1,258
Net charge-offs	(1,151)	(1,137)		(3,835)	(3,774)
Provision (benefit) for loan and lease losses	1,087	1,031		3,571	3,658
Allowance build (release) for loan and lease losses	(64)	(106)		(264)	(116)
Other changes	(8)	2		(1)	(12)
Balance at end of the period	5,270	5,520	5,624	5,270	5,520
Credit Card | Reserve for unfunded lending commitments
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period	0	0		0	0
Provision (benefit) for loan and lease losses	0	0		0	0
Balance at end of the period	0	0	0	0	0
Credit Card | Combined allowance and reserve
Allowance for Loan and Lease Losses [Roll Forward]
Balance at end of the period	5,270	5,520		5,270	5,520
Consumer Banking
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period	1,055	1,120		1,048	1,242
Charge-offs	(489)	(469)		(1,383)	(1,314)
Recoveries	238	207		739	631
Net charge-offs	(251)	(262)		(644)	(683)
Provision (benefit) for loan and lease losses	203	185		603	538
Allowance build (release) for loan and lease losses	(48)	(77)		(41)	(145)
Other changes	0	0		0	(54)
Balance at end of the period	1,007	1,043	1,120	1,007	1,043
Consumer Banking | Reserve for unfunded lending commitments
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period	4	5		4	7
Provision (benefit) for loan and lease losses	0	(1)		0	(3)
Balance at end of the period	4	4	5	4	4
Consumer Banking | Combined allowance and reserve
Allowance for Loan and Lease Losses [Roll Forward]
Balance at end of the period	1,011	1,047		1,011	1,047
Consumer Banking | Home loan
Allowance for Loan and Lease Losses [Roll Forward]
Net charge-offs	0	0		0	1
Commercial Banking
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period	736	624		637	611
Charge-offs	(66)	(48)		(109)	(76)
Recoveries	6	21		19	37
Net charge-offs	(60)	(27)		(90)	(39)
Provision (benefit) for loan and lease losses	84	60		213	85
Allowance build (release) for loan and lease losses	24	33		123	46
Other changes	0	(1)		0	(1)
Balance at end of the period	760	656	624	760	656
Commercial Banking | Reserve for unfunded lending commitments
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period	140	112		118	117
Provision (benefit) for loan and lease losses	9	(6)		31	(11)
Balance at end of the period	149	106	112	149	106
Commercial Banking | Combined allowance and reserve
Allowance for Loan and Lease Losses [Roll Forward]
Balance at end of the period	$ 909	762		$ 909	762
Other
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period		0			1
Charge-offs		1			(7)
Recoveries		0			1
Net charge-offs		1			(6)
Provision (benefit) for loan and lease losses		(1)			(49)
Allowance build (release) for loan and lease losses		0			(55)
Other changes		0			54
Balance at end of the period		0	0		0
Other | 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		0
Other | Combined allowance and reserve
Allowance for Loan and Lease Losses [Roll Forward]
Balance at end of the period		$ 0			$ 0
Other | Home loan
Allowance for Loan and Lease Losses [Roll Forward]
Provision (benefit) for credit losses			$ (46)