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Description Of The Business And Summary Of Significant Accounting Policies (Narrative) (Details) shares in Millions, $ in Millions	4 Months Ended	8 Months Ended	12 Months Ended
	Apr. 30, 2021 USD ($) shares	Dec. 31, 2021 USD ($) continent country shares	Dec. 31, 2021 floater country continent jackup rigs	Dec. 31, 2020 USD ($) shares	Dec. 31, 2019 USD ($) shares
Description Of The Business And Summary Of Significant Accounting Policies [Line Items]
Number of contract drilling rigs \| rigs			56
Number of different countries having drilling contracts spanning \| country		14	14
Number of different continents having drilling contracts \| continent		6	6
Net foreign currency exchange gains (losses) \| $	$ 13.4	$ 8.1		$ (11.0)	$ (7.4)
Asset Impairment Charges \| $	$ 756.5	$ 0.0		$ 3,646.2	$ 104.0
Antidilutive share options excluded from computation of diluted earnings per share \| shares	0.3	0.6		0.4	0.3
Drilling rigs and equipment [Member] \| Minimum
Description Of The Business And Summary Of Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life			5 years
Drilling rigs and equipment [Member] \| Maximum
Description Of The Business And Summary Of Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life			35 years
Building and Building Improvements [Member] \| Minimum
Description Of The Business And Summary Of Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life			10 years
Building and Building Improvements [Member] \| Maximum
Description Of The Business And Summary Of Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life			30 years
Equipment [Member] \| Minimum
Description Of The Business And Summary Of Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life			2 years
Equipment [Member] \| Maximum
Description Of The Business And Summary Of Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life			6 years
Other Rigs [Member]
Description Of The Business And Summary Of Significant Accounting Policies [Line Items]
Asset Impairment Charges \| $	$ 756.5			$ 3,600.0	$ 98.4
Floaters [Member] \| Ultra Deepwater Drillships [Member]
Description Of The Business And Summary Of Significant Accounting Policies [Line Items]
Number of contract drilling rigs			11
Floaters [Member] \| Dynamically Positioned Semisubmersible [Member]
Description Of The Business And Summary Of Significant Accounting Policies [Line Items]
Number of contract drilling rigs			4
Floaters [Member] \| Moored Semisubmersible Rigs [Member]
Description Of The Business And Summary Of Significant Accounting Policies [Line Items]
Number of contract drilling rigs			1
Jackups [Member]
Description Of The Business And Summary Of Significant Accounting Policies [Line Items]
Number of contract drilling rigs \| jackup			40
ARO
Description Of The Business And Summary Of Significant Accounting Policies [Line Items]
Number of contract drilling rigs			7