Condensed Consolidated Statements of Cash Flows - USD ($) $ in Millions		6 Months Ended
		Mar. 31, 2022	Mar. 31, 2021
Cash flows from operating activities:
Net income		$ 105.7	$ 74.8
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization		20.4	17.0
Amortization of right of use assets		7.8	4.8
Bad debt expense, net		12.1	2.4
Deferred income taxes		(0.4)	4.2
Amortization of debt issuance costs		2.2	2.1
Amortization of share-based compensation		8.3	6.5
Changes in operating assets and liabilities, net:
Securities and other assets segregated under federal and other regulations		(11.5)	(89.6)
Securities purchased under agreements to resell		(290.7)	(601.0)
Securities borrowed		78.3	(295.3)
Deposits with and receivables from broker-dealers, clearing organizations, and counterparties, net		202.3	(189.5)
Receivables from clients, net		(126.7)	(78.6)
Notes receivable, net		1.0	(5.0)
Income taxes receivable		10.6	1.3
Financial instruments owned, at fair value		198.4	(185.4)
Physical commodities inventory, net		(134.5)	(169.7)
Other assets		6.8	(22.5)
Accounts payable and other accrued liabilities		31.6	10.0
Operating lease liabilities		(6.8)	(3.2)
Payables to clients		1,661.9	855.3
Payables to broker-dealers, clearing organizations, and counterparties		(93.6)	(16.8)
Income taxes payable		15.4	(6.0)
Securities sold under agreements to repurchase		(533.0)	611.7
Securities loaned		(49.9)	305.3
Financial instruments sold, not yet purchased, at fair value		986.3	432.2
Net cash provided by operating activities		2,102.0	665.0
Cash flows from investing activities:
Cash paid for acquisitions, net		0.0	(0.4)
Sale of exchange memberships and common stock		0.2	0.0
Purchases of property and equipment		(24.3)	(40.0)
Net cash used in investing activities		(24.1)	(40.4)
Cash flows from financing activities:
Net change in payables to lenders under loans with maturities 90 days or less		232.7	42.8
Proceeds from payables to lenders under loans with maturities greater than 90 days		430.0	120.4
Repayments of payables to lenders under loans with maturities greater than 90 days		(440.0)	(125.4)
Repayments of senior secured term loan		(4.9)	(4.9)
Issuance of note payable		0.0	9.0
Deferred payments on acquisitions		(1.5)	(0.8)
Exercise of stock options		5.9	5.3
Net cash provided by financing activities		222.2	46.4
Effect of exchange rates on cash, segregated cash, cash equivalents, and segregated cash equivalents		(0.1)	12.7
Net increase in cash, segregated cash, cash equivalents, and segregated cash equivalents		2,300.0	683.7
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		8,809.5	5,152.1
Supplemental disclosure of cash flow information:
Cash paid for interest		43.9	32.9
Income taxes paid, net of cash refunds		7.8	28.2
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		1,299.7	1,001.5
Cash segregated under federal and other regulations	[1]	2,740.9	2,000.3
Cash segregated and deposited with or pledged to exchange-clearing organizations and other futures commission merchants (“FCMs”)	[2]	4,294.1	2,050.3
Securities segregated and pledged to exchange-clearing organizations	[2]	474.8	100.0
Total cash, segregated cash, cash equivalents, and segregated cash equivalents shown in the condensed consolidated statements of cash flows		8,809.5	5,152.1
Non-cash equivalent segregated assets		25.6	102.6
Non-segregated cash and other non-cash equivalent assets included within deposits and receivables from broker-dealers, clearing organizations, and counterparties		$ 1,951.0	$ 2,210.9

[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 $25.6 million and $102.6 million as of March 31, 2022 and 2021, 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 $1,951.0 million and $2,210.9 million as of March 31, 2022 and 2021, respectively, included within Deposits with and receivables from broker-dealers, clearing organizations, and counterparties, net on the Condensed Consolidated Balance Sheets.