Debt (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Nov. 16, 2020	Sep. 11, 2020	Jan. 17, 2020	Dec. 31, 2019	May 24, 2019	Feb. 01, 2019	Oct. 25, 2018	Jul. 31, 2018
Principal amount
Total installments of debt	$ 7,376				$ 9,361
Debt due within one year	449				581
Long-term debt	6,927				8,780
Carrying amount
Total debt	7,807				9,261
Debt due within one year	505				568
Long-term debt	$ 7,302				8,693
Transocean Inc
Carrying amount
Percentage ownership interest in Transocean Inc. by Transocean Ltd.	100.00%
6.50% Senior Notes due November 2020
Principal amount
Total installments of debt					206
Debt due within one year					206
Carrying amount
Total debt					206
Debt due within one year					206
Debt instrument interest rate stated percentage	6.50%	6.50%
6.375% Senior Notes due December 2021
Principal amount
Total installments of debt	$ 38				222
Carrying amount
Total debt	38				221
Debt due within one year	$ 38
Debt instrument interest rate stated percentage	6.375%
5.52% Senior Secured Notes due May 2022
Principal amount
Total installments of debt	$ 111				200
Debt due within one year	93				88
Carrying amount
Total debt	111				198
Debt due within one year	$ 92				87
Debt instrument interest rate stated percentage	5.52%
3.80% Senior Notes due October 2022
Principal amount
Total installments of debt	$ 27				190
Carrying amount
Total debt	$ 27				189
Debt instrument interest rate stated percentage	3.80%
0.50% Exchangeable Senior Bonds due January 2023
Principal amount
Total installments of debt	$ 463				863
Carrying amount
Total debt	$ 462				862
Debt instrument interest rate stated percentage	0.50%
5.375% Senior Secured Notes due May 2023
Principal amount
Total installments of debt	$ 364				525
Debt due within one year	47				16
Carrying amount
Total debt	360				518
Debt due within one year	$ 46				14
Debt instrument interest rate stated percentage	5.375%					5.375%
9.00% Senior Notes due July 2023
Principal amount
Total installments of debt					714
Carrying amount
Total debt					701
Debt instrument interest rate stated percentage	9.00%
5.875% Senior Secured Notes due January 2024
Principal amount
Total installments of debt	$ 585				667
Debt due within one year	83				83
Carrying amount
Total debt	577				656
Debt due within one year	$ 80				79
Debt instrument interest rate stated percentage	5.875%								5.875%
7.75% Senior Secured Notes due October 2024
Principal amount
Total installments of debt	$ 360				420
Debt due within one year	60				60
Carrying amount
Total debt	354				412
Debt due within one year	$ 58				58
Debt instrument interest rate stated percentage	7.75%
6.25% Senior Secured Notes due December 2024
Principal amount
Total installments of debt	$ 375				437
Debt due within one year	62				62
Carrying amount
Total debt	369				430
Debt due within one year	$ 60				60
Debt instrument interest rate stated percentage	6.25%
6.125% Senior Secured Notes due August 2025
Principal amount
Total installments of debt	$ 468				534
Debt due within one year	66				66
Carrying amount
Total debt	461				525
Debt due within one year	$ 64				64
Debt instrument interest rate stated percentage	6.125%								6.125%
7.25% Senior Notes due November 2025
Principal amount
Total installments of debt	$ 411				750
Carrying amount
Total debt	$ 405				737
Debt instrument interest rate stated percentage	7.25%							7.25%
7.50% Senior Notes due January 2026
Principal amount
Total installments of debt	$ 569				750
Carrying amount
Total debt	$ 565				743
Debt instrument interest rate stated percentage	7.50%
2.50% Senior Guaranteed Exchangeable Bonds due January 2027
Principal amount
Total installments of debt	$ 238
Carrying amount
Total debt	277
Debt due within one year	$ 6
Debt instrument interest rate stated percentage	2.50%
11.50% Senior Guaranteed Notes due January 2027
Principal amount
Total installments of debt	$ 687
Carrying amount
Total debt	1,139
Debt due within one year	$ 61
Debt instrument interest rate stated percentage	11.50%		11.50%
6.875% Senior Secured Notes due February 2027
Principal amount
Total installments of debt	$ 550				550
Carrying amount
Total debt	$ 542				541
Debt instrument interest rate stated percentage	6.875%						6.875%
8.00% Senior Notes due February 2027
Principal amount
Total installments of debt	$ 612
Carrying amount
Total debt	$ 606
Debt instrument interest rate stated percentage	8.00%			8.00%
7.45% Notes due April 2027
Principal amount
Total installments of debt	$ 52				88
Carrying amount
Total debt	$ 51				86
Debt instrument interest rate stated percentage	7.45%
8.00% Debentures due April 2027
Principal amount
Total installments of debt	$ 22				57
Carrying amount
Total debt	$ 22				57
Debt instrument interest rate stated percentage	8.00%
7.00% Notes due June 2028
Principal amount
Total installments of debt	$ 261				300
Carrying amount
Total debt	$ 266				306
Debt instrument interest rate stated percentage	7.00%
7.50% Notes due April 2031
Principal amount
Total installments of debt	$ 396				588
Carrying amount
Total debt	$ 394				585
Debt instrument interest rate stated percentage	7.50%
6.80% Senior Notes due March 2038
Principal amount
Total installments of debt	$ 610				1,000
Carrying amount
Total debt	$ 605				991
Debt instrument interest rate stated percentage	6.80%
7.35% Senior Notes due December 2041
Principal amount
Total installments of debt	$ 177				300
Carrying amount
Total debt	$ 176				$ 297
Debt instrument interest rate stated percentage	7.35%