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Debt (Issuance) (Details) - USD ($) $ in Millions		1 Months Ended	9 Months Ended
Debt (Issuance) (Details) - USD ($) $ in Millions	Oct. 15, 2025	Apr. 30, 2024	Sep. 30, 2024	Oct. 31, 2025	Sep. 30, 2025	Jun. 30, 2024
Debt
Proceeds from issuance of debt		$ 1,770	$ 1,767
Orion/Transocean Norge \| Orion/Transocean Norge
Debt
Equity ownership (as a percent)						67.00%
8.00% Senior Notes due February 2027
Debt
Debt instrument interest rate stated percentage			8.00%		8.00%	8.00%
8.00% Senior Notes due February 2027 \| Subsequent Event
Debt
Debt instrument interest rate stated percentage				8.00%
8.00% Senior Notes due February 2027 \| Orion/Transocean Norge
Debt
Debt instrument interest rate stated percentage						8.00%
8.00% Senior Notes due February 2027 \| Orion/Transocean Norge
Debt
Debt instrument face value						$ 130
Debt instrument interest rate stated percentage						8.00%
8.25% Senior Notes due May 2029
Debt
Debt instrument face value		$ 900
Debt instrument interest rate stated percentage		8.25%			8.25%
8.50% Senior Notes due May 2031
Debt
Debt instrument face value		$ 900
Debt instrument interest rate stated percentage		8.50%			8.50%
7.875% Senior Guaranteed Notes due October 2032. \| Subsequent Event
Debt
Debt instrument face value	$ 500
Debt instrument interest rate stated percentage	7.875%
Proceeds from issuance of debt	$ 492
7.875% Senior Guaranteed Notes due October 2032. \| Subsequent Event \| Redemption of up to 40% of principal amount of debt
Debt
Redemption price of debt instrument (as a percent)	107.875%
7.875% Senior Guaranteed Notes due October 2032. \| Subsequent Event \| Redemption of all or a portion of principal amount of debt
Debt
Redemption price of debt instrument (as a percent)	100.00%
7.875% Senior Guaranteed Notes due October 2032. \| Subsequent Event \| Maximum \| Redemption of up to 40% of principal amount of debt
Debt
Principal amount of debt redeemed (as a percent)	40.00%