Condensed Consolidated Statements of Cash Flows - USD ($) $ in Millions		3 Months Ended
		Dec. 31, 2021	Dec. 31, 2020
Cash flows from operating activities:
Net income		$ 41.7	$ 19.5
Adjustments to reconcile net income to net cash used in operating activities:
Depreciation and amortization		9.1	8.4
Amortization of right of use assets		3.8	2.8
Bad debt (recovery)/expense		(0.2)	1.5
Deferred income taxes		(0.5)	0.2
Amortization of debt issuance costs		1.0	1.0
Amortization of share-based compensation		4.1	3.1
Changes in operating assets and liabilities, net:
Securities and other assets segregated under federal and other regulations		2.5	2.8
Securities purchased under agreements to resell		(123.7)	(239.4)
Securities borrowed		(585.1)	212.2
Deposits with and receivables from broker-dealers, clearing organizations, and counterparties, net		(564.7)	(350.8)
Receivables from clients, net		(66.7)	153.9
Notes receivable, net		(0.7)	(3.0)
Income taxes receivable		3.9	(4.5)
Financial instruments owned, at fair value		654.0	(124.7)
Physical commodities inventory, net		(76.4)	(158.0)
Other assets		(4.8)	(7.1)
Accounts payable and other accrued liabilities		(15.8)	(27.8)
Operating lease liabilities		(2.9)	(1.6)
Payables to clients		201.7	202.0
Payables to broker-dealers, clearing organizations, and counterparties		(260.1)	(222.7)
Income taxes payable		5.9	(3.7)
Securities sold under agreements to repurchase		(249.2)	479.8
Securities loaned		593.5	(204.1)
Financial instruments sold, not yet purchased, at fair value		(170.6)	141.4
Net cash used in operating activities		(600.2)	(118.8)
Cash flows from investing activities:
Cash paid for acquisitions, net		0.0	(0.4)
Purchase of property and equipment		(7.3)	(22.4)
Net cash used in investing activities		(7.3)	(22.8)
Cash flows from financing activities:
Net change in payables to lenders under loans with maturities 90 days or less		230.9	91.5
Proceeds from payables to lenders under loans with maturities greater than 90 days		71.0	67.0
Repayments of payables to lenders under loans with maturities greater than 90 days		(61.0)	(62.0)
Repayments of senior secured term loan		(2.5)	(2.4)
Issuance of note payable		0.0	9.0
Deferred payments on acquisitions		(1.5)	(0.3)
Exercise of stock options		4.6	1.7
Net cash provided by financing activities		241.5	104.5
Effect of exchange rates on cash, segregated cash, cash equivalents, and segregated cash equivalents		(1.5)	14.1
Net decrease in cash, segregated cash, cash equivalents, and segregated cash equivalents		(367.5)	(23.0)
Cash, segregated cash, cash equivalents, and segregated cash equivalents at beginning of period		6,509.5	4,468.4
Cash, segregated cash, cash equivalents, and segregated cash equivalents at end of period		6,142.0	4,445.4
Supplemental disclosure of cash flow information:
Cash paid for interest		28.5	27.5
Income taxes paid, net of cash refunds		1.3	14.4
Supplemental disclosure of non-cash investing and financing activities:
Identified intangible assets and goodwill on acquisitions		0.0	0.5
Acquisition of business:
Assets acquired		0.0	0.1
Liabilities assumed		0.0	(0.2)
Total net liabilities assumed		0.0	(0.1)
Cash and cash equivalents		983.4	1,033.7
Cash segregated under federal and other regulations	[1]	2,100.2	2,193.7
Cash segregated and deposited with or pledged to exchange-clearing organizations and other futures commission merchants (“FCMs”)	[2]	3,058.4	1,208.4
Securities segregated and pledged to exchange-clearing organizations	[2]	0.0	9.6
Total cash, segregated cash, cash equivalents, and segregated cash equivalents shown in the condensed consolidated statements of cash flows		6,142.0	4,445.4
Non-cash equivalent segregated assets		11.5	10.2
Non-segregated cash and other non-cash equivalent assets included within deposits and receivables from broker-dealers, clearing organizations, and counterparties		$ 2,718.0	$ 2,372.1

[1] Represents segregated client cash held at third-party banks. Excludes segregated commodity warehouse receipts, segregated U.S. Treasury obligations with original or acquired maturities of greater than 90 days, and other assets of $11.5 million and $10.2 million as of December 31, 2021 and 2020, respectively, included within Cash, securities and other assets segregated under federal and other regulations on the Condensed Consolidated Balance Sheets.

[2] Represents segregated client cash and U.S. Treasury obligations on deposit with, or pledged to, exchange clearing organizations and other FCMs. Excludes non-segregated cash, segregated U.S. Treasury obligations pledged to exchange-clearing organizations with original or acquired maturities greater than 90 days, and other assets of $2,718.0 million and $2,372.1 million as of December 31, 2021 and 2020, respectively, included within Deposits with and receivables from broker-dealers, clearing organizations, and counterparties, net on the Condensed Consolidated Balance Sheets.