Loans and Allowance for Credit Losses - Impaired Loans Average Recorded Investment and Interest Income Recognized (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Mar. 31, 2019	Dec. 31, 2018
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	$ 4,643	$ 4,920
Interest Income Recognized	47	40
Commercial [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	485	545
Interest Income Recognized	1	1
Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	273	267
Interest Income Recognized	2	2
Residential Mortgages [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	1,697	1,914
Interest Income Recognized	24	20
Other Retail [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	330	300
Interest Income Recognized	3	4
Credit Card [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	249	232
Interest Income Recognized		1
Covered Loans [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment		38
Total Loans, Excluding Loans Purchased from GNMA Mortgage Pools [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	3,034	3,296
Interest Income Recognized	30	28
Government National Mortgage Association [Member]
Financing Receivable, Impaired [Line Items]
Average Recorded Investment	1,609	1,624
Interest Income Recognized	$ 17	$ 12

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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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://fasb.org/us-gaap/role/ref/legacyRef
-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://fasb.org/us-gaap/role/ref/legacyRef
-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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