Allowance for Loan and Lease Losses and Reserve for Unfunded Lending Commitments - Allowance for Loan and Lease Losses and Reserve for Unfunded Lending Commitments Activity (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Jun. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period		$ 7,220
Allowance build (release) for loan and lease losses	$ (68)
Balance at end of the period		7,208	$ 7,220
Provision (benefit) for credit losses		(6,236)	(5,856)	$ (7,551)
Allowance
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period		7,220	7,502	6,503
Charge-offs		(8,809)	(8,615)	(8,513)
Recoveries		2,557	2,503	1,951
Net charge-offs		(6,252)	(6,112)	(6,562)
Provision (benefit) for loan and lease losses		6,223	5,858	7,563
Allowance build (release) for loan and lease losses		(29)	(254)	1,001
Other changes		17	(28)	(2)
Balance at end of the period		7,208	7,220	7,502
Reserve for unfunded lending commitments
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period		122	124	136
Provision (benefit) for loan and lease losses		13	(2)	(12)
Balance at end of the period		135	122	124
Combined allowance and reserve
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period		7,342	7,626
Balance at end of the period		7,343	7,342	7,626
Credit Card
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period		5,535	5,648	4,606
Charge-offs		(6,711)	(6,657)	(6,321)
Recoveries		1,562	1,588	1,267
Net charge-offs		(5,149)	(5,069)	(5,054)
Provision (benefit) for loan and lease losses		4,992	4,984	6,066
Allowance build (release) for loan and lease losses		(157)	(85)	1,012
Other changes		17	(28)	30
Balance at end of the period		5,395	5,535	5,648
Credit Card \| Reserve for unfunded lending commitments
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period		0	0	0
Provision (benefit) for loan and lease losses		0	0	0
Balance at end of the period		0	0	0
Credit Card \| Combined allowance and reserve
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period		5,535	5,648
Balance at end of the period		5,395	5,535	5,648
Consumer Banking
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period		1,048	1,242	1,102
Charge-offs		(1,917)	(1,832)	(1,677)
Recoveries		970	851	639
Net charge-offs		(947)	(981)	(1,038)
Provision (benefit) for loan and lease losses		937	841	1,180
Allowance build (release) for loan and lease losses		(10)	(140)	142
Other changes		0	(54)	(2)
Balance at end of the period		1,038	1,048	1,242
Consumer Banking \| Reserve for unfunded lending commitments
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period		4	7	7
Provision (benefit) for loan and lease losses		1	(3)	0
Balance at end of the period		5	4	7
Consumer Banking \| Combined allowance and reserve
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period		1,052	1,249
Balance at end of the period		1,043	1,052	1,249
Commercial Banking
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period		637	611	793
Charge-offs		(181)	(119)	(481)
Recoveries		25	63	16
Net charge-offs		(156)	(56)	(465)
Provision (benefit) for loan and lease losses		294	82	313
Allowance build (release) for loan and lease losses		138	26	(152)
Other changes		0	0	(30)
Balance at end of the period		775	637	611
Commercial Banking \| Reserve for unfunded lending commitments
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period		118	117	129
Provision (benefit) for loan and lease losses		12	1	(12)
Balance at end of the period		130	118	117
Commercial Banking \| Combined allowance and reserve
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period		755	728
Balance at end of the period		905	755	728
Other
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period		0	1	2
Charge-offs			(7)	(34)
Recoveries			1	29
Net charge-offs			(6)	(5)
Provision (benefit) for loan and lease losses			(49)	4
Allowance build (release) for loan and lease losses			(55)	(1)
Other changes			54	0
Balance at end of the period			0	1
Other \| Reserve for unfunded lending commitments
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period		0	0	0
Provision (benefit) for loan and lease losses			0	0
Balance at end of the period			0	0
Other \| Combined allowance and reserve
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period		0	1
Balance at end of the period			0	1
Other
Allowance for Loan and Lease Losses [Roll Forward]
Provision (benefit) for credit losses		$ 0	49	$ (4)
Other \| Home loan portfoilio
Allowance for Loan and Lease Losses [Roll Forward]
Gain (loss) on sale of home loan portfolio			499
Provision (benefit) for credit losses			$ (46)

Allowance for Loan and Lease Losses and Reserve for Unfunded Lending Commitments - Allowance for Loan and Lease Losses and Reserve for Unfunded Lending Commitments Activity (Detail) - USD ($)
$ in Millions

3 Months Ended

12 Months Ended

Jun. 30, 2019

Dec. 31, 2019

Dec. 31, 2018

Dec. 31, 2017

Allowance for Loan and Lease Losses [Roll Forward]

Balance as beginning of the period

$ 7,220

Allowance build (release) for loan and lease losses

$ (68)

Balance at end of the period