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Revenues (Disaggregation) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
Revenues (Disaggregation) (Details) - USD ($) $ in Millions	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Revenue
Recognized pre-operating costs	$ 23	$ 3	$ 32	$ 6
Unrecognized pre-operating costs	38		38		$ 34
Face amount of receivable	185		185
Performance obligations satisfied in previous periods	177		177	10
Contract drilling revenues	930	758	1,689	1,512
Ultra-deepwater floaters
Revenue
Contract drilling revenues	636	486	1,164	962
Harsh environment floaters
Revenue
Contract drilling revenues	293	251	513	509
Deepwater floaters
Revenue
Contract drilling revenues		1		7
Midwater floaters
Revenue
Contract drilling revenues	1	20	12	34
U.S.
Revenue
Contract drilling revenues	440	309	727	623
U.S. \| Ultra-deepwater floaters
Revenue
Contract drilling revenues	440	309	727	623
Norway
Revenue
Contract drilling revenues	207	173	414	354
Norway \| Harsh environment floaters
Revenue
Contract drilling revenues	207	173	414	354
Brazil
Revenue
Contract drilling revenues	57	28	116	60
Brazil \| Ultra-deepwater floaters
Revenue
Contract drilling revenues	57	28	116	54
Brazil \| Deepwater floaters
Revenue
Contract drilling revenues				6
Other
Revenue
Contract drilling revenues	226	248	432	475
Other \| Ultra-deepwater floaters
Revenue
Contract drilling revenues	139	149	321	285
Other \| Harsh environment floaters
Revenue
Contract drilling revenues	86	78	99	155
Other \| Deepwater floaters
Revenue
Contract drilling revenues		1		1
Other \| Midwater floaters
Revenue
Contract drilling revenues	1	$ 20	12	$ 34
Accounts receivable
Revenue
Receivable net of discount	89		89
Other assets
Revenue
Receivable net of discount	$ 88		$ 88