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Revenues (Disaggregation) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
Revenues (Disaggregation) (Details) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Jun. 30, 2020	Dec. 31, 2019
Revenue
Recognized pre-operating costs	$ 16	$ 4	$ 48	$ 10
Unrecognized pre-operating costs	23		23			$ 34
Face amount of receivable					$ 185
Performance obligations satisfied in previous periods			177	10
Contract drilling revenues	773	784	2,462	2,296
Ultra-deepwater floaters
Revenue
Contract drilling revenues	490	493	1,654	1,455
Harsh environment floaters
Revenue
Contract drilling revenues	283	281	796	790
Deepwater floaters
Revenue
Contract drilling revenues				7
Midwater floaters
Revenue
Contract drilling revenues		10	12	44
U.S.
Revenue
Contract drilling revenues	295	321	1,022	944
U.S. \| Ultra-deepwater floaters
Revenue
Contract drilling revenues	295	317	1,022	940
U.S. \| Harsh environment floaters
Revenue
Contract drilling revenues		4		4
Norway
Revenue
Contract drilling revenues	233	200	647	554
Norway \| Harsh environment floaters
Revenue
Contract drilling revenues	233	200	647	554
Brazil
Revenue
Contract drilling revenues	60	27	176	87
Brazil \| Ultra-deepwater floaters
Revenue
Contract drilling revenues	60	27	176	81
Brazil \| Deepwater floaters
Revenue
Contract drilling revenues				6
Other
Revenue
Contract drilling revenues	185	236	617	711
Other \| Ultra-deepwater floaters
Revenue
Contract drilling revenues	135	149	456	434
Other \| Harsh environment floaters
Revenue
Contract drilling revenues	50	77	149	232
Other \| Deepwater floaters
Revenue
Contract drilling revenues				1
Other \| Midwater floaters
Revenue
Contract drilling revenues		$ 10	12	$ 44
Accounts receivable
Revenue
Receivable net of discount	89		89
Other assets
Revenue
Receivable net of discount	$ 88		$ 88