Postemployment Benefit Plans (Funded) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Change in projected benefit obligation
Projected benefit obligation, beginning of period	$ 2,108	$ 1,882
Actuarial (gains) losses, net	195	248
Service cost	1	7	$ 7
Interest cost	63	74	72
Currency exchange rate changes	9	14
Benefits paid	(98)	(93)
Settlements	(54)	(24)
Plan amendments	1
Projected benefit obligation, end of period	2,225	2,108	1,882
Change in plan assets
Fair value of plan assets, beginning of period	1,799	1,567
Actual return on plan assets	317	311
Currency exchange rate changes	6	16
Employer contributions	14	22	17
Benefits paid	(98)	(93)
Settlements	(53)	(24)
Fair value of plan assets, end of period	1,985	1,799	1,567
Funded status, end of period	(240)	(309)
Balance sheet classification, end of period:
Pension asset, non-current	37	42
Pension liability, current	(5)	(5)
Pension liability, non-current	(272)	(346)
Accumulated other comprehensive loss (income), before taxes	312	376
Accumulated benefit obligation, end of period	2,225	2,098
Aggregate projected benefit obligation and fair value of plan assets for plans with a projected benefit obligation in excess of plan assets
Projected benefit obligation	1,843	1,769
Fair value of plan assets	1,566	1,418
Aggregate accumulated benefit obligation and fair value of plan assets for plans with an accumulated benefit obligation in excess of plan assets
Accumulated benefit obligation	1,843	1,714
Fair value of plan assets	1,566	1,369
Accumulated other comprehensive income expected to be recognized during the next fiscal year
Actuarial loss, net	322	390
Prior service cost, net	(10)	(14)
Total amount expected to be recognized	312	376
Transocean Plans
Change in plan assets
Fair value of plan assets, beginning of period	1,799
Fair value of plan assets, end of period	$ 1,985	$ 1,799
Transocean Plans | U.S.
Weighted average assumptions used to determine benefit obligations
Discount rate (as a percent)	2.60%	3.27%
Expected long-term rate of return (as a percent)	5.51%	5.91%
Change in projected benefit obligation
Projected benefit obligation, beginning of period	$ 1,696	$ 1,527
Actuarial (gains) losses, net	148	202
Interest cost	55	63	61
Benefits paid	(72)	(72)
Settlements	(2)	(24)
Projected benefit obligation, end of period	1,825	1,696	1,527
Change in plan assets
Fair value of plan assets, beginning of period	1,369	1,189
Actual return on plan assets	267	272
Employer contributions	3	4
Benefits paid	(72)	(72)
Settlements	(2)	(24)
Fair value of plan assets, end of period	1,565	1,369	1,189
Funded status, end of period	(260)	(327)
Balance sheet classification, end of period:
Pension liability, current	(1)	(1)
Pension liability, non-current	(259)	(326)
Accumulated other comprehensive loss (income), before taxes	242	304
Accumulated benefit obligation, end of period	1,825	1,696
Aggregate projected benefit obligation and fair value of plan assets for plans with a projected benefit obligation in excess of plan assets
Projected benefit obligation	1,825	1,696
Fair value of plan assets	1,565	1,369
Aggregate accumulated benefit obligation and fair value of plan assets for plans with an accumulated benefit obligation in excess of plan assets
Accumulated benefit obligation	1,825	1,696
Fair value of plan assets	1,565	1,369
Accumulated other comprehensive income expected to be recognized during the next fiscal year
Actuarial loss, net	242	304
Total amount expected to be recognized	$ 242	$ 304
Transocean Plans | Non-U.S. Plans
Weighted average assumptions used to determine benefit obligations
Discount rate (as a percent)	1.50%	2.13%
Expected long-term rate of return (as a percent)	3.20%	3.18%
Change in projected benefit obligation
Projected benefit obligation, beginning of period	$ 395	$ 338
Actuarial (gains) losses, net	46	45
Service cost	1	7	7
Interest cost	8	10	10
Currency exchange rate changes	9	14
Benefits paid	(24)	(19)
Settlements	(52)
Plan amendments	1
Projected benefit obligation, end of period	384	395	338
Change in plan assets
Fair value of plan assets, beginning of period	430	378
Actual return on plan assets	50	39
Currency exchange rate changes	6	16
Employer contributions	9	16
Benefits paid	(24)	(19)
Settlements	(51)
Fair value of plan assets, end of period	420	430	378
Funded status, end of period	36	35
Balance sheet classification, end of period:
Pension asset, non-current	37	42
Pension liability, current	(1)	(1)
Pension liability, non-current		(6)
Accumulated other comprehensive loss (income), before taxes	80	84
Accumulated benefit obligation, end of period	384	385
Aggregate projected benefit obligation and fair value of plan assets for plans with a projected benefit obligation in excess of plan assets
Projected benefit obligation	2	56
Fair value of plan assets	1	49
Aggregate accumulated benefit obligation and fair value of plan assets for plans with an accumulated benefit obligation in excess of plan assets
Accumulated benefit obligation	2	1
Fair value of plan assets	1
Accumulated other comprehensive income expected to be recognized during the next fiscal year
Actuarial loss, net	78	84
Prior service cost, net	2
Total amount expected to be recognized	$ 80	$ 84
OPEB Plans
Weighted average assumptions used to determine benefit obligations
Discount rate (as a percent)	1.21%	2.39%
Change in projected benefit obligation
Projected benefit obligation, beginning of period	$ 17	$ 17
Actuarial (gains) losses, net	1	1
Interest cost		1	1
Benefits paid	(2)	(2)
Projected benefit obligation, end of period	16	17	$ 17
Change in plan assets
Employer contributions	2	2
Benefits paid	(2)	(2)
Funded status, end of period	(16)	(17)
Balance sheet classification, end of period:
Pension liability, current	(3)	(3)
Pension liability, non-current	(13)	(14)
Accumulated other comprehensive loss (income), before taxes	(10)	(12)
Accumulated benefit obligation, end of period	16	17
Aggregate projected benefit obligation and fair value of plan assets for plans with a projected benefit obligation in excess of plan assets
Projected benefit obligation	16	17
Aggregate accumulated benefit obligation and fair value of plan assets for plans with an accumulated benefit obligation in excess of plan assets
Accumulated benefit obligation	16	17
Accumulated other comprehensive income expected to be recognized during the next fiscal year
Actuarial loss, net	2	2
Prior service cost, net	(12)	(14)
Total amount expected to be recognized	$ (10)	$ (12)