Loans and Allowance for Credit Losses - Impaired Loans Average Recorded Investment and Interest Income Recognized (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	$ 5,316	$ 5,710	$ 6,160
Interest Income Recognized	204	237	274
Commercial [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	683	799	383
Interest Income Recognized	7	9	13
Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	273	324	433
Interest Income Recognized	11	15	16
Residential Mortgages [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	2,135	2,422	2,666
Interest Income Recognized	103	124	131
Other Retail [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	287	293	336
Interest Income Recognized	14	13	14
Credit Card [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	229	214	221
Interest Income Recognized	3	4	4
Total Loans, Excluding GNMA and Covered Loans [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	3,607	4,052	4,039
Interest Income Recognized	138	165	178
Covered Loans [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	37	38	42
Interest Income Recognized	1	1	1
Government National Mortgage Association [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	1,672	1,620	2,079
Interest Income Recognized	$ 65	$ 71	$ 95

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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=84173941&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=84173941&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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