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Drilling rigs
 12 Months Ended
Dec. 31, 2015
Property, Plant and Equipment [Abstract]  
Drilling rigs
Drilling units
 
(In US$ millions)
December 31,
2015
 
December 31,
2014
Cost
6,434.2

 
5,790.5

Accumulated depreciation
(886.9
)
 
(649.4
)
Net book value
5,547.3

 
5,141.1


Depreciation and amortization expense related to the drilling units was $237.5 million, $198.7 million and $141.2 million for the years ended December 31, 2015, 2014 and 2013 respectively.