Loans and Allowance for Credit Losses - Impaired Loans Average Recorded Investment and Interest Income Recognized (Detail) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	$ 5,466	$ 5,839	$ 5,494	$ 5,898
Interest Income Recognized	55	65	110	130
Commercial [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	720	842	769	756
Interest Income Recognized	1	3	2	4
Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	272	302	275	314
Interest Income Recognized	3	3	5	6
Residential Mortgages [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	2,182	2,452	2,211	2,496
Interest Income Recognized	28	31	57	63
Other Retail [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	279	297	279	301
Interest Income Recognized	3	3	7	6
Credit Card [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	229	212	227	211
Interest Income Recognized	1	1	2	2
Total Loans, Excluding GNMA and Covered Loans [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	3,682	4,105	3,761	4,078
Interest Income Recognized	36	41	73	81
Covered Loans [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	38	38	37	38
Interest Income Recognized		1		1
Government National Mortgage Association [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	1,746	1,696	1,696	1,782
Interest Income Recognized	$ 19	$ 23	$ 37	$ 48

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- Definition

Amount of average investment of impaired financing receivables for which there is a related allowance for credit losses.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=66008989&loc=d3e5212-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=66008989&loc=d3e5258-111524

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- Definition

Amount of interest income, recognized on accrual basis, on financing receivables, for which there is a related allowance for credit losses and are recognized as impaired.

+ References

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