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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				6 Months Ended
	Sep. 30, 2020	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Debt Instrument [Line Items]
Principal amount		$ 27,158,633,000				$ 27,158,633,000		$ 26,940,911,000
Long-term debt		26,989,068,000				26,989,068,000		26,722,342,000
Loss on extinguishment of debt and write-off of deferred financing costs		51,712,000		$ 0		51,712,000	$ 0
Stock Issued During Period, Value, New Issues		8,885,000	$ 2,044,000	$ 1,965,000	$ 2,507,000
Collateralized Agreements		122,176,000				122,176,000
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
Line of Credit Facility, Maximum Borrowing Capacity		100,000,000				100,000,000
Cablevision Lightpath Term B Loan \| Secured Debt [Member]
Debt Instrument [Line Items]
Principal amount		597,000,000				597,000,000		600,000,000
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		$ 25,857,440,000				$ 25,857,440,000		$ 25,685,115,000