Senior Notes and Other Long-Term Debt - Senior Notes (Detail) - USD ($) $ in Millions				3 Months Ended
	May 02, 2025	Sep. 30, 2024	Sep. 28, 2023	Jun. 30, 2025	Sep. 25, 2024	May 30, 2023	Jun. 30, 2020	Mar. 31, 2019	Sep. 30, 2017
2031 Notes [Member]
Debt Instrument [Line Items]
Principal amount of senior notes issued			$ 733.4
Debt maturity year			2031
Interest rate on the outstanding borrowings			7.50%
2031 Notes [Member] | Debt Instrument, Redemption, Other Period One [Member]
Debt Instrument [Line Items]
Redemption description of Senior Notes				Prior to May 30, 2026, the Company may redeem up to 40% of the 2031 Notes at a redemption price of 107.500% of the principal amount thereof, plus accrued and unpaid interest, if any, thereon to the redemption date, from the net cash proceeds of specified equity offerings.
Redemption price percentage of Senior Notes				107.50%
2031 Notes [Member] | Debt Instrument, Redemption, Period One [Member]
Debt Instrument [Line Items]
Redemption description of Senior Notes				The Company may also redeem the 2031 Notes prior to May 30, 2026, in whole or in part, at a redemption price equal to 100% of the principal amount thereof plus a “make whole” premium and any accrued and unpaid interest, if any, thereon to the redemption date.
Redemption price percentage of Senior Notes				100.00%
2031 Notes [Member] | Debt Instrument, Redemption, Period Two [Member]
Debt Instrument [Line Items]
Redemption description of Senior Notes				The 2031 Notes may be redeemed, in whole or in part, at any time during the 12 months beginning on May 30, 2026 at a redemption price of 103.750%
Redemption price percentage of Senior Notes				103.75%
2031 Notes [Member] | Debt Instrument, Redemption, Period Three [Member]
Debt Instrument [Line Items]
Redemption description of Senior Notes				during the 12 months beginning on May 30, 2027 at a redemption price of 101.875%
Redemption price percentage of Senior Notes				101.875%
2031 Notes [Member] | Debt Instrument, Redemption, Period Four [Member]
Debt Instrument [Line Items]
Redemption description of Senior Notes				at any time on or after May 30, 2028 at a redemption price of 100%, in each case plus accrued and unpaid interest, if any, thereon to the redemption date.
Redemption price percentage of Senior Notes				100.00%
2031 Notes [Member] | Change of Control [Member]
Debt Instrument [Line Items]
Redemption description of Senior Notes				In the event a change of control triggering event occurs (as defined in the indenture governing the 2031 Notes), each holder will have the right to require the Company to repurchase all or any part of such holder’s 2031 Notes at a purchase price in cash equal to 101% of the aggregate principal amount of the 2031 Notes repurchased, plus accrued and unpaid interest, if any, to the date of purchase (subject to the right of holders of record on the relevant record date to receive interest due on the relevant interest payment date).
Redemption price percentage of Senior Notes				101.00%
2028 Notes [Member]
Debt Instrument [Line Items]
Principal amount of senior notes issued							$ 400.0
Debt maturity year				2028
Interest rate on the outstanding borrowings				6.50%
2028 Notes [Member] | Debt Instrument, Redemption, Other Period One [Member]
Debt Instrument [Line Items]
Redemption description of Senior Notes				in whole or in part, at any time at a redemption price of 100% plus accrued and unpaid interest, if any, thereon to the redemption date.
2028 Notes [Member] | Debt Instrument, Redemption, Period Two [Member]
Debt Instrument [Line Items]
Redemption price percentage of Senior Notes				100.00%
2028 Notes [Member] | Change of Control [Member]
Debt Instrument [Line Items]
Redemption description of Senior Notes				In the event a change of control triggering event occurs (as defined in the indenture governing the 2028 Notes), each holder will have the right to require the Company to repurchase all or any part of such holder’s 2028 Notes at a purchase price in cash equal to 101% of the aggregate principal amount of the 2028 Notes repurchased, plus accrued and unpaid interest, if any, to the date of purchase (subject to the right of holders of record on the relevant record date to receive interest due on the relevant interest payment date).
Redemption price percentage of Senior Notes				101.00%
2027 Notes [Member]
Debt Instrument [Line Items]
Principal amount of senior notes issued								$ 600.0
Debt maturity year				2027
Interest rate on the outstanding borrowings				5.625%
2027 Notes [Member] | Debt Instrument, Redemption, Period One [Member]
Debt Instrument [Line Items]
Redemption description of Senior Notes				in whole or in part, at any time at a redemption price of 100% plus accrued and unpaid interest, if any, thereon to the redemption date.
Redemption price percentage of Senior Notes				100.00%
2027 Notes [Member] | Change of Control [Member]
Debt Instrument [Line Items]
Redemption description of Senior Notes				In the event a change of control triggering event occurs (as defined in the indenture governing the 2027 Notes), each holder will have the right to require the Company to repurchase all or any part of such holder’s 2027 Notes at a purchase price in cash equal to 101% of the aggregate principal amount of the 2027 Notes repurchased, plus accrued and unpaid interest, if any, to the date of purchase (subject to the right of holders of record on the relevant record date to receive interest due on the relevant interest payment date).
Redemption price percentage of Senior Notes				101.00%
2025 Notes [Member]
Debt Instrument [Line Items]
Principal amount of senior notes issued									$ 700.0
Debt maturity year				2025
Principal amount of senior notes repurchased	$ 442.6	$ 257.5
Interest rate on the outstanding borrowings				5.625%
Redemption price percentage of Senior Notes	100.00%
Inmarsat Senior Secured Notes 2029 [Member]
Debt Instrument [Line Items]
Principal amount of senior notes issued					$ 1,975.0
Debt maturity year		2029
Interest rate on the outstanding borrowings		9.00%
Inmarsat Senior Secured Notes 2029 [Member] | Debt Instrument, Redemption, Other Period One [Member]
Debt Instrument [Line Items]
Redemption description of Senior Notes				The issuers may also redeem the Inmarsat 2029 Notes prior to September 15, 2026, in whole or in part, at a redemption price equal to 100% of the principal amount thereof plus a “make-whole” premium and any accrued and unpaid interest, if any, thereon to the redemption date.
Redemption price percentage of Senior Notes				100.00%
Inmarsat Senior Secured Notes 2029 [Member] | Debt Instrument, Redemption, Period One [Member]
Debt Instrument [Line Items]
Redemption description of Senior Notes				Prior to September 15, 2026, the issuers may redeem up to 40% of the Inmarsat 2029 Notes at a redemption price 109.000% of the principal amount thereof, plus accrued and unpaid interest, if any, thereon to the redemption date, from the net cash proceeds of specified equity offerings so long as at least 50% of the aggregate principal amount of the Inmarsat 2029 Notes originally issued remains outstanding after such redemptions.
Redemption price percentage of Senior Notes				109.00%
Inmarsat Senior Secured Notes 2029 [Member] | Debt Instrument, Redemption, Period Two [Member]
Debt Instrument [Line Items]
Redemption description of Senior Notes				The Inmarsat 2029 Notes may be redeemed, in whole or in part, at any time during the 12 months beginning on September 15, 2026 at a redemption price of 104.500%
Redemption price percentage of Senior Notes				104.50%
Inmarsat Senior Secured Notes 2029 [Member] | Debt Instrument, Redemption, Period Three [Member]
Debt Instrument [Line Items]
Redemption description of Senior Notes				during the 12 months beginning on September 15, 2027 at a redemption price of 102.250%
Redemption price percentage of Senior Notes				102.25%
Inmarsat Senior Secured Notes 2029 [Member] | Debt Instrument, Redemption, Period Four [Member]
Debt Instrument [Line Items]
Redemption description of Senior Notes				at any time on or after September 15, 2028 at a redemption price of 100%, in each case plus accrued and unpaid interest, if any, thereon to the redemption date.
Redemption price percentage of Senior Notes				100.00%
Inmarsat Senior Secured Notes 2029 [Member] | Change of Control [Member]
Debt Instrument [Line Items]
Redemption description of Senior Notes				In the event a change of control occurs (as defined in the indenture governing the Inmarsat 2029 Notes), each holder will have the right to require the issuers to repurchase all or a portion of such holder’s Inmarsat 2029 Notes at a purchase price in cash equal to 101% of the aggregate principal amount of the Inmarsat 2029 Notes repurchased, plus accrued and unpaid interest, if any, to the date of purchase (subject to the right of holders of record on the relevant record date to receive interest due on the relevant interest payment date).
Redemption price percentage of Senior Notes				101.00%
Bridge Facility [Member]
Debt Instrument [Line Items]
Credit Facility maximum borrowing capacity						$ 733.4