Assets and Liabilities, at Fair Value - Financial Assets and Liabilities Measured at Fair Value (Details) - USD ($) $ in Millions	Mar. 31, 2023	Sep. 30, 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 25.8	$ 805.7
Securities and other assets segregated under federal and other regulations	2,512.3	3,267.2
Financial instruments owned	5,049.1	4,167.3
Physical commodities inventory	572.1	513.5
Accounts payable and other accrued liabilities	513.8	400.6
Payable to broker-dealers, clearing organizations and counterparties	558.4	659.8
Financial instruments sold, not yet purchased	2,570.9	2,469.6
Fair Value, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	81.9	43.5
Securities and other assets segregated under federal and other regulations	25.8	805.7
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net	4,655.7	2,817.2
Receivables from clients, net - Derivatives	2.3	(0.5)
Financial instruments owned	5,049.1	4,167.3
Total assets at fair value	10,166.4	8,193.0
Accounts payable and other accrued liabilities	1.3
Payables to clients - Derivatives	669.5	(1,392.4)
Total liabilities at fair value	3,275.8	1,133.0
Fair Value, Recurring | TBA and forward settling securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payable to broker-dealers, clearing organizations and counterparties	35.0	58.0
Fair Value, Recurring | Derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payable to broker-dealers, clearing organizations and counterparties	(0.9)	(2.2)
Fair Value, Recurring | Payable to broker-dealers, clearing organizations and counterparties
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payable to broker-dealers, clearing organizations and counterparties	34.1	55.8
Fair Value, Recurring | Physical commodities inventory
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Physical commodities inventory	351.6	359.8
Fair Value, Recurring | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	390.9	379.7
Financial instruments sold, not yet purchased	331.0	305.6
Fair Value, Recurring | Corporate and municipal bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	196.8	156.8
Financial instruments sold, not yet purchased	98.6	63.2
Fair Value, Recurring | U.S. Treasury obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	641.0	347.6
Financial instruments sold, not yet purchased	1,830.6	1,686.5
Fair Value, Recurring | U.S. government agency obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	334.1	343.0
Financial instruments sold, not yet purchased	13.8	24.3
Fair Value, Recurring | Foreign government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	4.1	4.8
Financial instruments sold, not yet purchased	5.9	0.5
Fair Value, Recurring | Agency mortgage-backed obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	3,021.4	2,588.7
Financial instruments sold, not yet purchased	40.8	5.4
Fair Value, Recurring | Asset-backed obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	75.8	70.7
Fair Value, Recurring | Derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	285.4	192.6
Financial instruments sold, not yet purchased	209.7	313.4
Fair Value, Recurring | Commodities leases
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	23.9	26.4
Fair Value, Recurring | Commodities warehouse receipts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	33.1	24.9
Fair Value, Recurring | Exchange firm common stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	11.5	10.6
Fair Value, Recurring | Cash flow hedges
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	4.7
Financial instruments sold, not yet purchased	38.5	70.6
Fair Value, Recurring | Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments sold, not yet purchased	2.0	0.1
Fair Value, Recurring | Mutual funds and other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	26.4	21.5
Fair Value, Recurring | TBA and forward settling securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net	14.3	116.2
Fair Value, Recurring | Foreign government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net	16.4	14.4
Fair Value, Recurring | U.S. Treasury obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net	4,153.3	4,258.5
Fair Value, Recurring | Derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net	471.7	(1,571.9)
Fair Value, Recurring | Commodities warehouse receipts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities and other assets segregated under federal and other regulations	25.7	19.7
Fair Value, Recurring | U.S. Treasury obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities and other assets segregated under federal and other regulations	0.1	786.0
Fair Value, Recurring | Certificates of deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	15.8	4.0
Fair Value, Recurring | Money market mutual funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	66.1	39.5
Fair Value, Recurring | Netting
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	0.0	0.0
Securities and other assets segregated under federal and other regulations	0.0	0.0
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net	(7,336.0)	(9,839.1)
Receivables from clients, net - Derivatives	(543.9)	(579.3)
Financial instruments owned	(616.7)	(502.4)
Total assets at fair value	(8,496.6)	(10,920.8)
Accounts payable and other accrued liabilities	0.0
Payables to clients - Derivatives	(5,972.7)	(9,290.3)
Financial instruments sold, not yet purchased	(555.5)	(466.3)
Total liabilities at fair value	(8,181.9)	(10,505.0)
Fair Value, Recurring | Netting | TBA and forward settling securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payable to broker-dealers, clearing organizations and counterparties	(37.5)	(96.9)
Fair Value, Recurring | Netting | Derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payable to broker-dealers, clearing organizations and counterparties	(1,616.2)	(651.5)
Fair Value, Recurring | Netting | Payable to broker-dealers, clearing organizations and counterparties
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payable to broker-dealers, clearing organizations and counterparties	(1,653.7)	(748.4)
Fair Value, Recurring | Netting | Physical commodities inventory
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Physical commodities inventory	0.0	0.0
Fair Value, Recurring | Netting | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0.0	0.0
Financial instruments sold, not yet purchased	0.0	0.0
Fair Value, Recurring | Netting | Corporate and municipal bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0.0	0.0
Financial instruments sold, not yet purchased	0.0	0.0
Fair Value, Recurring | Netting | U.S. Treasury obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0.0	0.0
Financial instruments sold, not yet purchased	0.0	0.0
Fair Value, Recurring | Netting | U.S. government agency obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0.0	0.0
Financial instruments sold, not yet purchased	0.0	0.0
Fair Value, Recurring | Netting | Foreign government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0.0	0.0
Financial instruments sold, not yet purchased	0.0	0.0
Fair Value, Recurring | Netting | Agency mortgage-backed obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0.0	0.0
Financial instruments sold, not yet purchased	0.0	0.0
Fair Value, Recurring | Netting | Asset-backed obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0.0	0.0
Fair Value, Recurring | Netting | Derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	(616.7)	(502.4)
Financial instruments sold, not yet purchased	(555.5)	(466.3)
Fair Value, Recurring | Netting | Commodities leases
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0.0	0.0
Fair Value, Recurring | Netting | Commodities warehouse receipts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0.0	0.0
Fair Value, Recurring | Netting | Exchange firm common stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0.0	0.0
Fair Value, Recurring | Netting | Cash flow hedges
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0.0
Financial instruments sold, not yet purchased	0.0	0.0
Fair Value, Recurring | Netting | Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments sold, not yet purchased	0.0	0.0
Fair Value, Recurring | Netting | Mutual funds and other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0.0	0.0
Fair Value, Recurring | Netting | TBA and forward settling securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net	(41.1)	(91.4)
Fair Value, Recurring | Netting | Foreign government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net	0.0	0.0
Fair Value, Recurring | Netting | U.S. Treasury obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net	0.0	0.0
Fair Value, Recurring | Netting | Derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net	(7,294.9)	(9,747.7)
Fair Value, Recurring | Netting | Commodities warehouse receipts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities and other assets segregated under federal and other regulations	0.0	0.0
Fair Value, Recurring | Netting | U.S. Treasury obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities and other assets segregated under federal and other regulations	0.0	0.0
Fair Value, Recurring | Netting | Certificates of deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	0.0	0.0
Fair Value, Recurring | Netting | Money market mutual funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	0.0	0.0
Fair Value, Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	81.9	43.5
Securities and other assets segregated under federal and other regulations	25.8	805.7
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net	10,674.8	11,987.3
Receivables from clients, net - Derivatives	50.8	67.2
Financial instruments owned	1,088.5	773.9
Total assets at fair value	12,033.3	13,813.9
Accounts payable and other accrued liabilities	0.0
Payables to clients - Derivatives	6,435.2	7,722.5
Financial instruments sold, not yet purchased	2,157.0	1,986.9
Total liabilities at fair value	8,702.1	9,768.1
Fair Value, Recurring | Level 1 | TBA and forward settling securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payable to broker-dealers, clearing organizations and counterparties	0.0	0.0
Fair Value, Recurring | Level 1 | Derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payable to broker-dealers, clearing organizations and counterparties	109.9	58.7
Fair Value, Recurring | Level 1 | Payable to broker-dealers, clearing organizations and counterparties
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payable to broker-dealers, clearing organizations and counterparties	109.9	58.7
Fair Value, Recurring | Level 1 | Physical commodities inventory
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Physical commodities inventory	111.5	136.3
Fair Value, Recurring | Level 1 | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	372.4	367.9
Financial instruments sold, not yet purchased	318.0	299.9
Fair Value, Recurring | Level 1 | Corporate and municipal bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0.0	0.0
Financial instruments sold, not yet purchased	0.0	0.0
Fair Value, Recurring | Level 1 | U.S. Treasury obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	641.0	347.6
Financial instruments sold, not yet purchased	1,830.6	1,686.5
Fair Value, Recurring | Level 1 | U.S. government agency obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0.0	0.0
Financial instruments sold, not yet purchased	0.0	0.0
Fair Value, Recurring | Level 1 | Foreign government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	4.1	4.8
Financial instruments sold, not yet purchased	5.9	0.5
Fair Value, Recurring | Level 1 | Agency mortgage-backed obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0.0	0.0
Financial instruments sold, not yet purchased	0.0	0.0
Fair Value, Recurring | Level 1 | Asset-backed obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0.0	0.0
Fair Value, Recurring | Level 1 | Derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0.6	0.7
Financial instruments sold, not yet purchased	2.5	0.0
Fair Value, Recurring | Level 1 | Commodities leases
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0.0	0.0
Fair Value, Recurring | Level 1 | Commodities warehouse receipts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	33.1	24.9
Fair Value, Recurring | Level 1 | Exchange firm common stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	11.5	10.6
Fair Value, Recurring | Level 1 | Cash flow hedges
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0.0
Financial instruments sold, not yet purchased	0.0	0.0
Fair Value, Recurring | Level 1 | Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments sold, not yet purchased	0.0	0.0
Fair Value, Recurring | Level 1 | Mutual funds and other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	25.8	17.4
Fair Value, Recurring | Level 1 | TBA and forward settling securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net	0.0	0.0
Fair Value, Recurring | Level 1 | Foreign government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net	16.4	14.4
Fair Value, Recurring | Level 1 | U.S. Treasury obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net	4,153.3	4,258.5
Fair Value, Recurring | Level 1 | Derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net	6,505.1	7,714.4
Fair Value, Recurring | Level 1 | Commodities warehouse receipts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities and other assets segregated under federal and other regulations	25.7	19.7
Fair Value, Recurring | Level 1 | U.S. Treasury obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities and other assets segregated under federal and other regulations	0.1	786.0
Fair Value, Recurring | Level 1 | Certificates of deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	15.8	4.0
Fair Value, Recurring | Level 1 | Money market mutual funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	66.1	39.5
Fair Value, Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	0.0	0.0
Securities and other assets segregated under federal and other regulations	0.0	0.0
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net	1,316.9	669.0
Receivables from clients, net - Derivatives	495.4	511.6
Financial instruments owned	4,576.7	3,895.8
Total assets at fair value	6,629.1	5,299.9
Accounts payable and other accrued liabilities	0.0
Payables to clients - Derivatives	207.0	175.4
Financial instruments sold, not yet purchased	968.2	949.0
Total liabilities at fair value	2,753.1	1,869.9
Fair Value, Recurring | Level 2 | TBA and forward settling securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payable to broker-dealers, clearing organizations and counterparties	72.5	154.9
Fair Value, Recurring | Level 2 | Derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payable to broker-dealers, clearing organizations and counterparties	1,505.4	590.6
Fair Value, Recurring | Level 2 | Payable to broker-dealers, clearing organizations and counterparties
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payable to broker-dealers, clearing organizations and counterparties	1,577.9	745.5
Fair Value, Recurring | Level 2 | Physical commodities inventory
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Physical commodities inventory	240.1	223.5
Fair Value, Recurring | Level 2 | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	18.5	11.8
Financial instruments sold, not yet purchased	13.0	5.7
Fair Value, Recurring | Level 2 | Corporate and municipal bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	196.8	156.8
Financial instruments sold, not yet purchased	98.6	63.2
Fair Value, Recurring | Level 2 | U.S. Treasury obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0.0	0.0
Financial instruments sold, not yet purchased	0.0	0.0
Fair Value, Recurring | Level 2 | U.S. government agency obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	334.1	343.0
Financial instruments sold, not yet purchased	13.8	24.3
Fair Value, Recurring | Level 2 | Foreign government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0.0	0.0
Financial instruments sold, not yet purchased	0.0	0.0
Fair Value, Recurring | Level 2 | Agency mortgage-backed obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	3,021.4	2,588.7
Financial instruments sold, not yet purchased	40.8	5.4
Fair Value, Recurring | Level 2 | Asset-backed obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	75.8	70.7
Fair Value, Recurring | Level 2 | Derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	901.5	694.3
Financial instruments sold, not yet purchased	762.7	779.7
Fair Value, Recurring | Level 2 | Commodities leases
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	23.9	26.4
Fair Value, Recurring | Level 2 | Commodities warehouse receipts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0.0	0.0
Fair Value, Recurring | Level 2 | Exchange firm common stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0.0	0.0
Fair Value, Recurring | Level 2 | Cash flow hedges
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	4.7
Financial instruments sold, not yet purchased	38.5	70.6
Fair Value, Recurring | Level 2 | Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments sold, not yet purchased	0.8	0.1
Fair Value, Recurring | Level 2 | Mutual funds and other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0.0	4.1
Fair Value, Recurring | Level 2 | TBA and forward settling securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net	55.4	207.6
Fair Value, Recurring | Level 2 | Foreign government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net	0.0	0.0
Fair Value, Recurring | Level 2 | U.S. Treasury obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net	0.0	0.0
Fair Value, Recurring | Level 2 | Derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net	1,261.5	461.4
Fair Value, Recurring | Level 2 | Commodities warehouse receipts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities and other assets segregated under federal and other regulations	0.0	0.0
Fair Value, Recurring | Level 2 | U.S. Treasury obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities and other assets segregated under federal and other regulations	0.0	0.0
Fair Value, Recurring | Level 2 | Certificates of deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	0.0	0.0
Fair Value, Recurring | Level 2 | Money market mutual funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	0.0	0.0
Fair Value, Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	0.0	0.0
Securities and other assets segregated under federal and other regulations	0.0	0.0
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net	0.0	0.0
Receivables from clients, net - Derivatives	0.0
Financial instruments owned	0.6	0.0
Total assets at fair value	0.6	0.0
Accounts payable and other accrued liabilities	1.3
Payables to clients - Derivatives	0.0
Financial instruments sold, not yet purchased	1.2	0.0
Total liabilities at fair value	2.5	0.0
Fair Value, Recurring | Level 3 | TBA and forward settling securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payable to broker-dealers, clearing organizations and counterparties	0.0	0.0
Fair Value, Recurring | Level 3 | Derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payable to broker-dealers, clearing organizations and counterparties	0.0	0.0
Fair Value, Recurring | Level 3 | Payable to broker-dealers, clearing organizations and counterparties
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payable to broker-dealers, clearing organizations and counterparties	0.0	0.0
Fair Value, Recurring | Level 3 | Physical commodities inventory
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Physical commodities inventory	0.0	0.0
Fair Value, Recurring | Level 3 | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0.0	0.0
Financial instruments sold, not yet purchased	0.0	0.0
Fair Value, Recurring | Level 3 | Corporate and municipal bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0.0	0.0
Financial instruments sold, not yet purchased	0.0	0.0
Fair Value, Recurring | Level 3 | U.S. Treasury obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0.0	0.0
Financial instruments sold, not yet purchased	0.0	0.0
Fair Value, Recurring | Level 3 | U.S. government agency obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0.0	0.0
Financial instruments sold, not yet purchased	0.0	0.0
Fair Value, Recurring | Level 3 | Foreign government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0.0	0.0
Financial instruments sold, not yet purchased	0.0	0.0
Fair Value, Recurring | Level 3 | Agency mortgage-backed obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0.0	0.0
Financial instruments sold, not yet purchased	0.0	0.0
Fair Value, Recurring | Level 3 | Asset-backed obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0.0	0.0
Fair Value, Recurring | Level 3 | Derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0.0	0.0
Financial instruments sold, not yet purchased	0.0	0.0
Fair Value, Recurring | Level 3 | Commodities leases
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0.0	0.0
Fair Value, Recurring | Level 3 | Commodities warehouse receipts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0.0	0.0
Fair Value, Recurring | Level 3 | Exchange firm common stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0.0	0.0
Fair Value, Recurring | Level 3 | Cash flow hedges
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0.0
Financial instruments sold, not yet purchased	0.0	0.0
Fair Value, Recurring | Level 3 | Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments sold, not yet purchased	1.2	0.0
Fair Value, Recurring | Level 3 | Mutual funds and other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0.6	0.0
Fair Value, Recurring | Level 3 | TBA and forward settling securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net	0.0	0.0
Fair Value, Recurring | Level 3 | Foreign government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net	0.0	0.0
Fair Value, Recurring | Level 3 | U.S. Treasury obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net	0.0	0.0
Fair Value, Recurring | Level 3 | Derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net	0.0	0.0
Fair Value, Recurring | Level 3 | Commodities warehouse receipts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities and other assets segregated under federal and other regulations	0.0	0.0
Fair Value, Recurring | Level 3 | U.S. Treasury obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities and other assets segregated under federal and other regulations	0.0	0.0
Fair Value, Recurring | Level 3 | Certificates of deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	0.0	0.0
Fair Value, Recurring | Level 3 | Money market mutual funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	$ 0.0	$ 0.0