Commitments, Guarantees, And Contingencies (Narrative) (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Loss Contingencies [Line Items]
Customer-owned securities pledged	$ 106.9	$ 39.2
Minimum margin deposit requirements	57.0
Outstanding committed capital to certain entities	26.7
Business Development Corporations [Member]
Loss Contingencies [Line Items]
Outstanding committed capital to certain entities	15.3
Options Clearing Corporation [Member]
Loss Contingencies [Line Items]
Customer-owned securities pledged	$ 57.1

Outstanding committed capital to certain entities.

No definition available.

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- Definition

Fair value as of the balance sheet date of customer securities accepted as collateral by the entity that it has sold or re-pledged to counterparties as collateral.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 30

-Section 50

-Paragraph 1A

-Subparagraph (c)(2)

-URI http://asc.fasb.org/extlink&oid=55761124&loc=SL6224234-111729

+ Details

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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.

+ Details

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- Definition

The amount of cash or securities placed with a broker or counterparty as security for a trading or derivatives securities position which was partially obtained with funds provided by the broker dealer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.8,17)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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- Details

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- Details

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