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Property and Equipment Property and Equipment (Schedule of Property and Equipment) (Details) $ in Millions	3 Months Ended			6 Months Ended		12 Months Ended
	Jun. 30, 2020 USD ($) floater	Mar. 31, 2020 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) rigs $ / bbl	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($) $ / bbl
Property, Plant and Equipment [Line Items]
PROPERTY AND EQUIPMENT, AT COST	$ 13,220.3			$ 13,220.3		$ 18,393.8
Asset Impairment Charges	$ 838.0		$ 2.5	$ 3,646.2	$ 2.5
Number of Rigs Impaired \| floater	2
Oil and Gas, Average Sale Price \| $ / bbl				20		60
Impairment of Long-Lived Assets to be Disposed of	$ 15.0
Number Of Rigs Held-for-Sale \| rigs				7
Assets Held-for-sale, Not Part of Disposal Group	20.9			$ 20.9		$ 2.3
Drilling rigs and equipment
Property, Plant and Equipment [Line Items]
PROPERTY AND EQUIPMENT, AT COST	12,559.5			12,559.5		17,714.0
Work-in-progress
Property, Plant and Equipment [Line Items]
PROPERTY AND EQUIPMENT, AT COST	473.2			473.2		473.6
Other
Property, Plant and Equipment [Line Items]
PROPERTY AND EQUIPMENT, AT COST	187.6			187.6		$ 206.2
Floaters, Jackups And Spare Equipment
Property, Plant and Equipment [Line Items]
Asset Impairment Charges	832.3			3,600.0
Impairment of Long-Lived Assets Held-for-use		$ 2,800.0
Property, Plant, and Equipment, Fair Value Disclosure		$ 72.3
Floaters And Spare Equipment
Property, Plant and Equipment [Line Items]
Impairment of Long-Lived Assets Held-for-use	817.3
Property, Plant, and Equipment, Fair Value Disclosure	$ 69.0			$ 69.0