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Equity (Share Issuance) (Details) - USD ($) shares in Millions, $ in Millions	1 Months Ended		3 Months Ended	9 Months Ended
	Sep. 30, 2025	Jun. 30, 2024	Sep. 30, 2025	Sep. 30, 2025
Equity
Issuance of shares (in shares)	143.8
Proceeds from issuance of shares, net of issue costs	$ 421			$ 421
Perestroika AS \| Related party
Equity
Issuance of shares (in shares)	4.0
Proceeds from issuance of shares, net of issue costs	$ 12
Perestroika AS \| Transocean Inc \| Director Affiliated with Perestroika Ltd. \| Related party
Equity
Ownership interest (as a percent)	10.00%		10.00%	10.00%
4.00% Senior Guaranteed Exchangeable Bonds due December 2025
Equity
Shares issued upon conversion (in shares)			54.7	73.3
Debt issued in exchange transactions			$ 147	$ 196
Debt instrument interest rate stated percentage	4.00%		4.00%	4.00%
Orion/Transocean Norge
Equity
Newly issued shares in asset acquisition (in shares)		55.5
Value shares issued in asset acquisition		$ 297
Orion/Transocean Norge \| Orion/Transocean Norge
Equity
Equity ownership (as a percent)		67.00%