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, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period	$ 6,503
Balance at end of the period	7,502	$ 6,503
Total Allowance
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period	6,503	5,130	$ 4,383
Charge-offs	(8,513)	(6,555)	(5,193)
Recoveries	1,951	1,493	1,498
Net charge-offs	(6,562)	(5,062)	(3,695)
Provision (benefit) for loan and lease losses	7,563	6,491	4,490
Allowance build (release) for loan and lease losses	1,001	1,429	795
Other changes	(2)	(56)	(48)
Balance at end of the period	7,502	6,503	5,130
Unfunded Lending Commitments Reserve
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period	136	168	113
Provision (benefit) for loan and lease losses	(12)	(32)	46
Other changes			9
Balance at end of the period	124	136	168
Combined Allowance & Unfunded Reserve
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period	6,639	5,298
Balance at end of the period	7,626	6,639	5,298
Credit Card Portfolio Segment [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period	4,606	3,654	3,204
Charge-offs	(6,321)	(5,019)	(4,028)
Recoveries	1,267	1,066	1,110
Net charge-offs	(5,054)	(3,953)	(2,918)
Provision (benefit) for loan and lease losses	6,066	4,926	3,417
Allowance build (release) for loan and lease losses	1,012	973	499
Other changes	30	(21)	(49)
Balance at end of the period	5,648	4,606	3,654
Credit Card Portfolio Segment [Member] | 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
Other changes			0
Balance at end of the period	0	0	0
Credit Card Portfolio Segment [Member] | Combined Allowance & Unfunded Reserve
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period	4,606	3,654
Balance at end of the period	5,648	4,606	3,654
Consumer Portfolio Segment [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period	1,102	868	779
Charge-offs	(1,677)	(1,226)	(1,082)
Recoveries	639	406	351
Net charge-offs	(1,038)	(820)	(731)
Provision (benefit) for loan and lease losses	1,180	1,055	819
Allowance build (release) for loan and lease losses	142	235	88
Other changes	(2)	(1)	1
Balance at end of the period	1,242	1,102	868
Consumer Portfolio Segment [Member] | 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	0	0	0
Other changes			0
Balance at end of the period	7	7	7
Consumer Portfolio Segment [Member] | Combined Allowance & Unfunded Reserve
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period	1,109	875
Balance at end of the period	1,249	1,109	875
Commercial Banking
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period	793	604	395
Charge-offs	(481)	(307)	(76)
Recoveries	16	15	29
Net charge-offs	(465)	(292)	(47)
Provision (benefit) for loan and lease losses	313	515	256
Allowance build (release) for loan and lease losses	(152)	223	209
Other changes	(30)	(34)	0
Balance at end of the period	611	793	604
Commercial Banking | Unfunded Lending Commitments Reserve
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period	129	161	106
Provision (benefit) for loan and lease losses	(12)	(32)	46
Other changes			9
Balance at end of the period	117	129	161
Commercial Banking | Combined Allowance & Unfunded Reserve
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period	922	765
Balance at end of the period	728	922	765
Other
Allowance for Loan and Lease Losses [Roll Forward]
Balance as beginning of the period	2	4	5
Charge-offs	(34)	(3)	(7)
Recoveries	29	6	8
Net charge-offs	(5)	3	1
Provision (benefit) for loan and lease losses	4	(5)	(2)
Allowance build (release) for loan and lease losses	(1)	(2)	(1)
Other changes	0	0	0
Balance at end of the period	1	2	4
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
Other changes			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	2	4
Balance at end of the period	$ 1	$ 2	$ 4