Fair Value Measurement and Election - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Transfer of Portfolio Loans and Leases to Held-for-sale	$ 204	$ 60
Loans Receivable, Fair Value Disclosure	188		$ 196
Unfunded loan commitments and letters of credit	68,300		66,400
Allowance for unfunded loan commitments and letters of credit	73		84
Total Return Swap [Member] \| Fair Value, Inputs, Level 2 [Member]
Loans Receivable, Fair Value Disclosure	1,700		1,700
Interest Rate Lock Commitments [Member]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3	(6)	$ 36
Trading Account Assets [Member] \| SBA Loans [Member] \| Fair Value, Inputs, Level 2 [Member]
Loans Receivable, Fair Value Disclosure	448		368
Trading Account Assets [Member] \| Commercial and Corporate Leveraged Loans [Member] \| Fair Value, Inputs, Level 2 [Member]
Loans Receivable, Fair Value Disclosure	74		48
Fair Value, Measurements, Recurring [Member]
Loans Receivable, Fair Value Disclosure	188		196
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member]
Loans Receivable, Fair Value Disclosure	0		0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member]
Loans Receivable, Fair Value Disclosure	0		0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member]
Loans Receivable, Fair Value Disclosure	$ 188		$ 196

Allowance for commercial unfunded loan commitments and letters of credit

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- Definition

Unfunded Commercial Loan Commitments and Letters of Credit

+ References

No definition available.

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- Definition

Amount of transfers of financial instrument classified as an asset out of level 3 of the fair value hierarchy.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(3)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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- Definition

Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-URI http://asc.fasb.org/subtopic&trid=2196772

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- Definition

Value of loans and leases held in the entity's portfolio transferred to loans and leases held-for-sale in noncash transactions.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4304-108586

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
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-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4332-108586

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4313-108586

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