NOTES PAYABLE, FINANCE LEASES, AND COMMERCIAL BANK FINANCING (Details) - USD ($)			1 Months Ended	3 Months Ended			9 Months Ended
	Nov. 06, 2025	Feb. 12, 2025	Oct. 31, 2025	Sep. 30, 2025	Jun. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024	Dec. 31, 2024	Feb. 07, 2023
Debt Instrument [Line Items]
Gain (loss) on extinguishment of debt				$ 0		$ 0	$ 6,000,000	$ 1,000,000
Interest Rate Swap
Debt Instrument [Line Items]
Notional amount										$ 600,000,000
Fixed interest rate										3.90%
Derivative liability				100,000			100,000
Derivative asset									$ 1,000,000
Guarantee Obligations
Debt Instrument [Line Items]
Unconditional and irrevocably guaranteed debt				2,000,000			2,000,000		2,000,000
Guarantee obligations, maximum amount				455,000,000			455,000,000
Guarantee obligations accrued payment							15,000,000
Guarantee Obligations | Accounts Payable and Accrued Liabilities
Debt Instrument [Line Items]
Guarantee obligations				8,000,000			8,000,000
Consolidated VIEs
Debt Instrument [Line Items]
Consolidated total debt				2,000,000			2,000,000		2,000,000
Affiliated Entity
Debt Instrument [Line Items]
Finance lease liabilities, current				3,000,000			3,000,000		3,000,000
Finance lease liabilities, non-current				$ 7,000,000			$ 7,000,000		$ 9,000,000
Line of Credit | First-Out Revolving Credit Facility
Debt Instrument [Line Items]
Maximum borrowing capacity		$ 575,000,000
Term Loan B-3 | Term Loan
Debt Instrument [Line Items]
Debt instrument, outstanding		711,400,000
Debt instrument, face amount		$ 714,000,000
Debt instrument, basis spread on variable rate		3.00%
Term Loan B-6, due December 31, 2029 | Term Loan
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate		3.30%
Term Loan B-4 | Term Loan
Debt Instrument [Line Items]
Debt instrument, face amount		$ 731,300,000
Debt instrument, basis spread on variable rate		3.75%
Term Loan B-7, due December 31, 2030 | Term Loan
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate		4.10%
First-Out Revolving Credit Facility | Line of Credit | First-Out Revolving Credit Facility
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate		2.00%
Maximum borrowing capacity		$ 575,000,000
First lien leverage ratio				3.5			3.5
Borrowings under revolving credit facility exceed total commitments (as a percent)							35.00%
Borrowings outstanding				$ 0			$ 0
Third Lien Obligations | Term Loan
Debt Instrument [Line Items]
Debt instrument, face amount		3,000,000
Third Lien Obligations | Line of Credit | First-Out Revolving Credit Facility
Debt Instrument [Line Items]
Maximum borrowing capacity		$ 75,000,000
STG Senior Unsecured Notes 8.125 Percent Due 2027 | Senior Notes
Debt Instrument [Line Items]
Debt instrument, face amount				$ 1,430,000,000			$ 1,430,000,000
Interest rate (as a percent)				8.125%			8.125%
STG Senior Unsecured Notes 8.125 Percent Due 2027 | Senior Notes | Debt Instrument, Redemption, Period One
Debt Instrument [Line Items]
Redemption price, percentage							100.00%
STG Senior Unsecured Notes 8.125 Percent Due 2027 | Senior Notes | Debt Instrument, Redemption, Period Two
Debt Instrument [Line Items]
Percentage of principal amount redeemed							40.00%
Redemption price, percentage							108.125%
STG Senior Unsecured Notes 8.125 Percent Due 2027 | Senior Notes | Debt Instrument, Redemption, Period Three
Debt Instrument [Line Items]
Redemption price, percentage							108.125%
Term Loan B-2 | Term Loan
Debt Instrument [Line Items]
Repayment of term loan							$ 1,175,000,000
Gain (loss) on extinguishment of debt							(6,000,000)
4.125% Senior Secured Notes due 2030 | Senior Notes
Debt Instrument [Line Items]
Debt instrument, face amount				$ 63,600,000			$ 63,600,000
Interest rate (as a percent)				4.125%			4.125%
Percentage of principal amount redeemed							84.00%
Gain (loss) on extinguishment of debt							$ 5,000,000
4.125% Senior Secured Notes due 2030 | Senior Notes | Debt Covenant Period One
Debt Instrument [Line Items]
Debt instrument, face amount				$ 432,000,000			432,000,000
4.125% Senior Secured Notes due 2030 | Senior Notes | Debt Covenant Period Two
Debt Instrument [Line Items]
Debt instrument, face amount				238,000,000			238,000,000
STG 5.125% Senior Notes | Senior Notes
Debt Instrument [Line Items]
Debt instrument, face amount				$ 104,000,000			$ 104,000,000
Interest rate (as a percent)				5.125%			5.125%
Percentage of principal amount redeemed							97.00%
Gain (loss) on extinguishment of debt							$ 3,000,000
Debt instrument, repurchased aggregate principal amount					$ 81,000,000
Repayments of debt					$ 77,000,000
STG 5.125% Senior Notes | Senior Notes | Subsequent Event
Debt Instrument [Line Items]
Debt instrument, repurchased aggregate principal amount			$ 89,000,000
Repayments of debt			$ 89,000,000
STG 5.125% Senior Notes | Senior Notes | Debt Instrument, Redemption, Period Four
Debt Instrument [Line Items]
Gain (loss) on extinguishment of debt							$ 4,000,000
STG Second Lien Secured Notes 9.750 Percent Due 2033 | Senior Notes
Debt Instrument [Line Items]
Interest rate (as a percent)				9.75%			9.75%
STG Second Lien Secured Notes 9.750 Percent Due 2033 | Senior Notes | Debt Instrument, Redemption, Period One
Debt Instrument [Line Items]
Redemption price, percentage							100.00%
STG Second Lien Secured Notes 9.750 Percent Due 2033 | Senior Notes | Debt Instrument, Redemption, Period Two
Debt Instrument [Line Items]
Percentage of principal amount redeemed							40.00%
Redemption price, percentage							109.75%
STG Second Lien Secured Notes 9.750 Percent Due 2033 | Senior Notes | Debt Instrument, Redemption, Period Three
Debt Instrument [Line Items]
Redemption price, percentage							109.75%
STG Second-Out First Lien Secured Notes 4.375 Percent due 2032 | Senior Notes
Debt Instrument [Line Items]
Interest rate (as a percent)				4.375%			4.375%
STG Second-Out First Lien Secured Notes 4.375 Percent due 2032 | Senior Notes | Debt Instrument, Redemption, Period One
Debt Instrument [Line Items]
Redemption price, percentage							100.00%
STG 4.125% Unsecured Notes due 2030 | Senior Notes
Debt Instrument [Line Items]
Interest rate (as a percent)				4.125%			4.125%
STG 4.125% Unsecured Notes due 2030 | Unsecured Debt
Debt Instrument [Line Items]
Debt instrument, face amount				$ 4,000,000			$ 4,000,000
Term Loan B-2, due September 30, 2026 | Term Loan
Debt Instrument [Line Items]
Repayment of term loan								25,000,000
Gain (loss) on extinguishment of debt								1,000,000
Debt instrument, repurchased aggregate principal amount						$ 27,000,000		$ 27,000,000
AR Facility | Line of Credit | First-Out Revolving Credit Facility | Subsequent Event
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 375,000,000
Term	3 years