Fair Value Measurement and Election - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Transfer of Portfolio Loans and Leases to Held-for-sale	$ 288	$ 360	$ 1,790
Estimated Fair Value of Loan Portfolio's Net Carrying Value, Percentage	101.00%	101.00%
Loans Receivable, Fair Value Disclosure	$ 196	$ 222
Unfunded loan commitments and letters of credit	66,400	67,200
Allowance for unfunded loan commitments and letters of credit	84	71
Total Return Swap [Member] \| Fair Value, Inputs, Level 2 [Member]
Loans Receivable, Fair Value Disclosure	1,700	2,100
Interest Rate Lock Commitments [Member]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3	191	211
Trading Account Assets [Member] \| SBA Loans [Member] \| Fair Value, Inputs, Level 2 [Member]
Loans Receivable, Fair Value Disclosure	368	310
Trading Account Assets [Member] \| Commercial and Corporate Leveraged Loans [Member] \| Fair Value, Inputs, Level 2 [Member]
Loans Receivable, Fair Value Disclosure	48	46
Fair Value, Measurements, Recurring [Member]
Loans Receivable, Fair Value Disclosure	196	222
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	$ 196	$ 222

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- Definition

Percentage of Carrying Value

+ References

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- Definition

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+ References

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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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