Revenues (Disaggregation) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Jun. 30, 2020
Revenue
Face amount of receivable						$ 185
Performance obligations satisfied in previous periods				$ 177
Receivable net of discount	$ 89		$ 89		$ 133
Recognized pre-operating costs	13	$ 16	43	48
Unrecognized pre-operating costs	6		6		20
Contract drilling revenues	626	773	1,935	2,462
Ultra-deepwater floaters
Revenue
Contract drilling revenues	428	490	1,288	1,654
Harsh environment floaters
Revenue
Contract drilling revenues	198	283	647	796
Midwater floaters
Revenue
Contract drilling revenues				12
U.S.
Revenue
Contract drilling revenues	280	295	823	1,022
U.S. | Ultra-deepwater floaters
Revenue
Contract drilling revenues	280	295	819	1,022
U.S. | Harsh environment floaters
Revenue
Contract drilling revenues			4
Norway
Revenue
Contract drilling revenues	185	233	609	647
Norway | Harsh environment floaters
Revenue
Contract drilling revenues	185	233	609	647
Other
Revenue
Contract drilling revenues	161	245	503	793
Other | Ultra-deepwater floaters
Revenue
Contract drilling revenues	148	195	469	632
Other | Harsh environment floaters
Revenue
Contract drilling revenues	13	$ 50	34	149
Other | Midwater floaters
Revenue
Contract drilling revenues				$ 12
Accounts receivable
Revenue
Receivable net of discount	46		46		45
Other assets, non-current
Revenue
Receivable net of discount	$ 43		$ 43		$ 88