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Drilling units (Tables)
 12 Months Ended
Dec. 31, 2019
Property, Plant and Equipment [Abstract]  
Drilling units
The below table shows the gross value and net book value of our drilling units at December 31, 2019 and December 31, 2018.
(In US$ millions)
Cost
 
Accumulated depreciation

 
Net Book Value
Opening balance as at January 1, 2018
6,599.0

 
(1,428.1
)
 
5,170.9

Additions
115.0

 
—

 
115.0

Depreciation
—

 
(280.3
)
 
(280.3
)
Closing balance as at December 31, 2018
6,714.0

 
(1,708.4
)
 
5,005.6

Additions
111.1

 
—

 
111.1

Depreciation
—

 
(275.9
)
 
(275.9
)
Closing balance as at December 31, 2019
6,825.1

 
(1,984.3
)
 
4,840.8