Allowance for Loan and Lease Losses - Components of Allowance for Loan and Lease Losses by Impairment Methodology (Detail) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for loan and lease losses by impairment methodology:
Collectively evaluated	$ 6,882	$ 7,044
Asset-specific	338	421
Total allowance for loan and lease losses	7,220	7,502
Loans held for investment by impairment methodology:
Collectively evaluated	243,920	241,323
Asset-specific	1,844	2,375
Loans held for investment	$ 245,899	$ 254,473	$ 245,586
Allowance as a percentage of period-end loans held for investment	2.94%	2.95%
Credit Card Portfolio Segment
Allowance for loan and lease losses by impairment methodology:
Collectively evaluated	$ 5,258	$ 5,356
Asset-specific	277	292
Total allowance for loan and lease losses	5,535	5,648	4,606	$ 3,654
Loans held for investment by impairment methodology:
Collectively evaluated	115,505	113,948
Asset-specific	855	812
Loans held for investment	$ 116,361	$ 114,762
Allowance as a percentage of period-end loans held for investment	4.76%	4.92%
Consumer Portfolio Segment
Allowance for loan and lease losses by impairment methodology:
Collectively evaluated	$ 1,021	$ 1,158
Asset-specific	27	53
Total allowance for loan and lease losses	1,048	1,242	1,102	868
Loans held for investment by impairment methodology:
Collectively evaluated	58,808	64,080
Asset-specific	393	705
Loans held for investment	$ 59,205	$ 75,078
Allowance as a percentage of period-end loans held for investment	1.77%	1.65%
Commercial Banking
Allowance for loan and lease losses by impairment methodology:
Collectively evaluated	$ 603	$ 529
Asset-specific	34	76
Total allowance for loan and lease losses	637	611	793	604
Loans held for investment by impairment methodology:
Collectively evaluated	69,607	63,237
Asset-specific	596	858
Loans held for investment	$ 70,333	$ 64,575
Allowance as a percentage of period-end loans held for investment	0.91%	0.95%
Other
Allowance for loan and lease losses by impairment methodology:
Collectively evaluated		$ 1
Asset-specific		0
Total allowance for loan and lease losses	$ 0	1	$ 2	$ 4
Loans held for investment by impairment methodology:
Collectively evaluated		58
Asset-specific		0
Loans held for investment		$ 58
Allowance as a percentage of period-end loans held for investment		1.72%
Financial Asset Acquired with Credit Deterioration [Member]
Allowance for loan and lease losses by impairment methodology:
Financing Receivable, Allowance for Credit Losses		$ 37
Loans held for investment by impairment methodology:
Loans held for investment	135	10,775
Financial Asset Acquired with Credit Deterioration [Member] | Credit Card Portfolio Segment
Allowance for loan and lease losses by impairment methodology:
Financing Receivable, Allowance for Credit Losses		0
Loans held for investment by impairment methodology:
Loans held for investment	1	2
Financial Asset Acquired with Credit Deterioration [Member] | Consumer Portfolio Segment
Allowance for loan and lease losses by impairment methodology:
Financing Receivable, Allowance for Credit Losses		31
Loans held for investment by impairment methodology:
Loans held for investment	4	10,293
Financial Asset Acquired with Credit Deterioration [Member] | Commercial Banking
Allowance for loan and lease losses by impairment methodology:
Financing Receivable, Allowance for Credit Losses		6
Loans held for investment by impairment methodology:
Loans held for investment	$ 130	480
Financial Asset Acquired with Credit Deterioration [Member] | Other
Allowance for loan and lease losses by impairment methodology:
Financing Receivable, Allowance for Credit Losses		0
Loans held for investment by impairment methodology:
Loans held for investment		$ 0