Certain Regulatory Requirements and Capital Ratios - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Banking Subsidiary Reserve Requirement	$ 1,900	$ 1,800
Yearly Average
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Banking Subsidiary Reserve Requirement	1,800	$ 1,700
Trust Preferred Securities
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier I capital (to risk-weighted assets)	$ 13
TruPS as a basis point percentage of risk-weighted assets	1

TruPS expressed as a basis point percentage of risk-weighted assets

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- Definition

Cash deposited in a special reserve account for the exclusive benefit of customers pursuant to SEC Regulations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 305
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6478312&loc=d3e61473-112792

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- Definition

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.

+ References

No definition available.

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- Definition

Tier 1 Risk Based Capital as defined in the regulations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1H
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=35709795&loc=d3e65071-112826

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