Condensed Consolidated Cash Flows Statements Reconciliation of Cash, Segregated Cash, Cash Equivalents, and Segregated Cash Equivalents - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Reconciliation of Cash, Segregated Cash, Cash Equivalents, and Segregated Cash Equivalents [Abstract]
Cash and cash equivalents	$ 338.9	$ 358.2
Cash segregated under federal and other regulations(1)	1,073.9	707.3
Securities segregated under federal and other regulations(1)	300.0	0.0
Cash segregated and deposited with or pledged to exchange-clearing organizations and other futures commissions merchants	993.0	959.5
Securities segregated and pledged to exchange-clearing organizations(2)	363.7	26.8
Cash, segregated cash, cash equivalents, and segregated cash equivalents at end of period	$ 3,069.0	$ 2,051.8

Deposits with and Receivables From Clearing Organizations, Segregated under Commodity Exchange Act Regulation

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- Definition

Reconciliation of Cash, Segregated Cash, Cash Equivalents, and Segregated Cash Equivalents [Abstract]

+ References

No definition available.

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- Definition

Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Excludes cash and cash equivalents within disposal group and discontinued operation.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.1)
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Amount of cash and cash equivalents, and cash and cash equivalents restricted to withdrawal or usage. Excludes amount for disposal group and discontinued operations. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 24
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-Topic 230
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- Definition

Cash deposited in a special reserve account for the exclusive benefit of customers pursuant to the Commodity Exchange Act.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-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

Fair value of securities deposited in a special reserve account for the exclusive benefit of customers pursuant to the Commodity Exchange Act.

+ References

No definition available.

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- Definition

Fair value of securities deposited in a special reserve account for the exclusive benefit of customers pursuant to regulations other than SEC Regulations and the Commodity Exchange Act.

+ References

No definition available.

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