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The total of collateralized agreements including securities purchased under agreements to resell (repos), borrowed securities, and secured demand notes.

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Percentage points added to the reference rate to compute the variable rate on the debt instrument.

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Face (par) amount of debt instrument at time of issuance.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Difference between the fair value of payments made and the carrying amount of debt which is extinguished prior to maturity.

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Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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The parent entity's interest in net assets of the subsidiary, expressed as a percentage.

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Equity impact of the value of new stock issued during the period. Includes shares issued in an initial public offering or a secondary public offering.

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DEBT - Senior Guaranteed Notes, Senior Secured Notes, and Senior Notes and Debentures (Details) - USD ($)	1 Months Ended	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Debt Instrument [Line Items]
Principal amount		$ 26,917,870,000						$ 26,917,870,000		$ 26,940,911,000
Long-term debt		26,771,563,000						26,771,563,000		26,722,342,000
Loss on extinguishment of debt and write-off of deferred financing costs		0			$ 250,489,000			51,712,000	$ 250,489,000
Stock Issued During Period, Value, New Issues		2,958,000	$ 8,885,000	$ 2,044,000	$ 2,392,000	$ 1,965,000	$ 2,507,000
Collateralized Agreements		75,125,000						75,125,000
Notes Payable that will be reclassed to collateralized debt upon maturity		$ 59,451,000						$ 59,451,000
Cablevision Lightpath LLC \| Cablevision Lightpath LLC
Debt Instrument [Line Items]
Ownership percentage of noncontrolling interest		50.01%						50.01%
CSC Holdings Revolving Credit Facility, Portion Due October 9, 2020 \| Revolving Credit Facility
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		$ 200,000						$ 200,000
Cablevision Lightpath Revolving Credit Facility \| Revolving Credit Facility
Debt Instrument [Line Items]
Principal amount		0						0		0
Cablevision Lightpath Term B Loan \| Secured Debt [Member]
Debt Instrument [Line Items]
Principal amount		595,500,000						595,500,000		600,000,000
Line of Credit Facility, Maximum Borrowing Capacity		100,000,000						100,000,000
Cablevision Lightpath Term B Loan \| Secured Debt [Member] \| Alternate Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate	2.25%
Cablevision Lightpath Term B Loan \| Secured Debt [Member] \| Eurodollar
Debt Instrument [Line Items]
Basis spread on variable rate	3.25%
Senior Notes \| CSC Holdings 5.750% Notes due January 15, 2030
Debt Instrument [Line Items]
Principal amount		$ 2,250,000,000						$ 2,250,000,000		2,250,000,000
Stated interest rate		5.75%						5.75%
Senior Notes \| CSC Holdings 4.500% Senior Guaranteed Notes due November 15, 2021
Debt Instrument [Line Items]
Principal amount		$ 1,500,000,000						$ 1,500,000,000
Stated interest rate		4.50%						4.50%
Senior Notes \| CSC Holdings 5.000% Notes due November 15, 2031
Debt Instrument [Line Items]
Principal amount		$ 500,000,000						$ 500,000,000
Stated interest rate		5.00%						5.00%
Secured Debt [Member] \| 5.5% Notes due April 15, 2027
Debt Instrument [Line Items]
Principal amount		$ 1,310,000,000						$ 1,310,000,000		1,310,000,000
Stated interest rate		5.50%						5.50%
Secured Debt [Member] \| CSC Holdings 5.500% Notes due May 15, 2026
Debt Instrument [Line Items]
Principal amount		$ 0						$ 0		1,498,806,000
Stated interest rate		5.50%						5.50%
Long-term Debt
Debt Instrument [Line Items]
Principal amount		$ 25,008,244,000						$ 25,008,244,000		$ 25,685,115,000