Fair Value Measurement and Election - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Loans Receivable, Fair Value Disclosure	$ 163	$ 196
Unfunded loan commitments and letters of credit	72,000	66,400
Allowance for unfunded loan commitments and letters of credit	72	84
Reclassification of Equity Securities from Nommarketable to Marketable	22
Fair Value, Inputs, Level 1 [Member]
Loans Receivable, Fair Value Disclosure	0	0
Fair Value, Inputs, Level 2 [Member]
Loans Receivable, Fair Value Disclosure	0	0
Fair Value, Inputs, Level 3 [Member]
Loans Receivable, Fair Value Disclosure	163	196
Total Return Swap [Member] \| Fair Value, Inputs, Level 2 [Member]
Loans Receivable, Fair Value Disclosure	2,000	1,700
Interest Rate Lock Commitments [Member]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3	63	191
Trading Loans [Member] \| SBA Loans [Member] \| Fair Value, Inputs, Level 2 [Member]
Loans Receivable, Fair Value Disclosure	366	368
Trading Loans [Member] \| Commercial and Corporate Leveraged Loans [Member] \| Fair Value, Inputs, Level 2 [Member]
Loans Receivable, Fair Value Disclosure	137	48
Fair Value, Measurements, Recurring [Member]
Loans Receivable, Fair Value Disclosure	163	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	$ 163	$ 196

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- Definition

Reclassification of Equity Securities from Nommarketable to Marketable

+ 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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(3)
-URI http://asc.fasb.org/extlink&oid=99377789&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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-URI http://asc.fasb.org/subtopic&trid=2196772

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