Allowance for Loan and Lease Losses - Summary of Changes in Allowance for Loan and Lease Losses (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period	$ 7,502
Balance at end of the period	7,220	$ 7,502
Benefit for credit losses	5,856	7,551	$ 6,459
Total Allowance
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period	7,502	6,503	5,130
Charge-offs	(8,615)	(8,513)	(6,555)
Recoveries	2,503	1,951	1,493
Net charge-offs	(6,112)	(6,562)	(5,062)
Provision (benefit) for loan and lease losses	5,858	7,563	6,491
Allowance build (release) for loan and lease losses	(254)	1,001	1,429
Other changes	(28)	(2)	(56)
Balance at end of the period	7,220	7,502	6,503
Unfunded Lending Commitments Reserve
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period	124	136	168
Provision (benefit) for loan and lease losses	(2)	(12)	(32)
Balance at end of the period	122	124	136
Combined Allowance & Unfunded Reserve
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period	7,626	6,639
Balance at end of the period	7,342	7,626	6,639
Credit Card Portfolio Segment
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period	5,648	4,606	3,654
Charge-offs	(6,657)	(6,321)	(5,019)
Recoveries	1,588	1,267	1,066
Net charge-offs	(5,069)	(5,054)	(3,953)
Provision (benefit) for loan and lease losses	4,984	6,066	4,926
Allowance build (release) for loan and lease losses	(85)	1,012	973
Other changes	(28)	30	(21)
Balance at end of the period	5,535	5,648	4,606
Credit Card Portfolio Segment | Unfunded Lending Commitments Reserve
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 Portfolio Segment | Combined Allowance & Unfunded Reserve
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period	5,648	4,606
Balance at end of the period	5,535	5,648	4,606
Consumer Portfolio Segment
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period	1,242	1,102	868
Charge-offs	(1,832)	(1,677)	(1,226)
Recoveries	851	639	406
Net charge-offs	(981)	(1,038)	(820)
Provision (benefit) for loan and lease losses	841	1,180	1,055
Allowance build (release) for loan and lease losses	(140)	142	235
Other changes	(54)	(2)	(1)
Balance at end of the period	1,048	1,242	1,102
Consumer Portfolio Segment | Unfunded Lending Commitments Reserve
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period	7	7	7
Provision (benefit) for loan and lease losses	(3)	0	0
Balance at end of the period	4	7	7
Consumer Portfolio Segment | Combined Allowance & Unfunded Reserve
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period	1,249	1,109
Balance at end of the period	1,052	1,249	1,109
Consumer Portfolio Segment | Home loan
Allowance for Loan and Lease Losses [Roll Forward]
Net charge-offs	1	(15)	(14)
Commercial Banking
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period	611	793	604
Charge-offs	(119)	(481)	(307)
Recoveries	63	16	15
Net charge-offs	(56)	(465)	(292)
Provision (benefit) for loan and lease losses	82	313	515
Allowance build (release) for loan and lease losses	26	(152)	223
Other changes	0	(30)	(34)
Balance at end of the period	637	611	793
Commercial Banking | Unfunded Lending Commitments Reserve
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period	117	129	161
Provision (benefit) for loan and lease losses	1	(12)	(32)
Balance at end of the period	118	117	129
Commercial Banking | Combined Allowance & Unfunded Reserve
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period	728	922
Balance at end of the period	755	728	922
Other
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period	1	2	4
Charge-offs	(7)	(34)	(3)
Recoveries	1	29	6
Net charge-offs	(6)	(5)	3
Provision (benefit) for loan and lease losses	(49)	4	(5)
Allowance build (release) for loan and lease losses	(55)	(1)	(2)
Other changes	54	0	0
Balance at end of the period	0	1	2
Other | Unfunded Lending Commitments Reserve
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
Other | Combined Allowance & Unfunded Reserve
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period	1	2
Balance at end of the period	0	1	2
Other
Allowance for Loan and Lease Losses [Roll Forward]
Benefit for credit losses	(49)	$ 4	$ (5)
Other | Consumer Portfolio Segment | Home loan
Allowance for Loan and Lease Losses [Roll Forward]
Gain (Loss) on Sale of Mortgage Loans	499
Benefit for credit losses	(46)
Other | Home Loans Receivable
Allowance for Loan and Lease Losses [Roll Forward]
Gain (Loss) on Sale of Mortgage Loans	499
Benefit for credit losses	$ 46