Consolidated Statements of Cash Flows - USD ($) $ in Millions		9 Months Ended
		Jun. 30, 2021	Jun. 30, 2020
Operating Activities
Net income (loss)	[1]	$ (150.3)	$ (152.8)
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Depreciation and amortization	[1]	134.9	330.5
Stock-based compensation	[1]	17.6	13.3
Certain interest expense and other financing costs	[1]	7.5	8.6
Loss on debt extinguishment	[1]	60.2	14.7
Gain on sale of fixed assets and other	[1]	(2.7)	(2.0)
Deferred income taxes	[1]	(163.9)	(41.2)
Loss on sale of Interior Products	[1],[2]	362.0	0.0
338(h)(10) election refund	[1]	0.0	(5.3)
Changes in operating assets and liabilities:
Accounts receivable	[1]	(67.0)	113.3
Inventories	[1]	(310.1)	65.8
Prepaid expenses and other current assets	[1]	(1.3)	4.8
Accounts payable and accrued expenses	[1],[3]	91.3	(102.5)
Other assets and liabilities	[1]	1.4	3.2
Net cash provided by (used in) operating activities	[1]	(20.4)	250.4
Investing Activities
Purchases of property and equipment	[1]	(47.4)	(31.4)
Acquisition of businesses, net	[1]	0.0	5.3
Proceeds from sale of Interior Products	[1],[2]	837.4	0.0
Proceeds from the sale of assets	[1]	3.1	2.4
Net cash provided by (used in) investing activities	[1]	793.1	(23.7)
Financing Activities
Borrowings under revolving lines of credit	[1]	252.3	2,037.2
Payments under revolving lines of credit	[1]	(509.3)	(1,271.2)
Borrowings under term loan	[1]	1,000.0	0.0
Payments under term loan	[1]	(945.8)	(7.3)
Borrowings under senior notes	[1]	350.0	300.0
Payment under senior notes	[1]	(1,300.0)	(309.6)
Payment of debt issuance costs	[1]	(20.3)	(3.9)
Payment of call premium	[1]	(31.7)	0.0
Payments under equipment financing facilities and finance leases	[1]	(4.9)	(6.4)
Payment of dividends on Preferred Stock	[1]	(18.0)	(18.0)
Proceeds from issuance of common stock related to equity awards	[1]	24.8	1.6
Payment of taxes related to net share settlement of equity awards	[1]	(4.5)	(2.8)
Net cash provided by (used in) financing activities	[1]	(1,207.4)	719.6
Effect of exchange rate changes on cash and cash equivalents	[1]	(1.0)	(0.2)
Net increase (decrease) in cash and cash equivalents	[1]	(435.7)	946.1
Cash and cash equivalents, beginning of period	[1]	624.6	72.3
Cash and cash equivalents, end of period	[1]	188.9	1,018.4
Supplemental Cash Flow Information
Operating cash flows provided by (used in) discontinued operations	[1]	(28.2)	84.3
Investing cash flows provided by (used in) discontinued operations	[1]	(2.5)	(6.9)
Cash paid during the period for:
Interest	[1]	105.7	116.2
Income taxes paid (received), net of refunds	[1],[4]	54.6	(0.4)
Supplemental Disclosure of Non-Cash Investing and Financing Activities
Finance lease liabilities arising from obtaining right-of-use assets	[1]	$ 19.5	$ 4.1

[1] Unless otherwise noted, amounts include both continuing and discontinued operations.

[2] See Note 3 for additional information.

[3] Nine months ended June 30, 2021 amount includes $48.1 million of cash collected on behalf of, and due to, Foundation Building Materials Holding Company LLC as part of an ongoing transaction services agreement. For additional information see Note 1.

[4] Nine months ended June 30, 2021 amount includes $46.6 million related to the Interior Products divestiture.