Supplemental Financial Information (Details Textuals) (USD $) In Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Dec. 31, 2010	Dec. 31, 2009
Supplemental financial information (Textuals) [Abstract]
Amount of bad debts recorded in prior periods and subsequently recovered	$ 1.7	$ 2.8	$ 10.1	$ 3.9
Interest paid on long-term debt			41.5	42.0
First installment of new drillship due					154.4
Interest on Internal Revenue Service Assessment				0.9
Capital expenditures accrued but unpaid			6.8		28.9	64.9
Amount of trade accounts receivable written off against allowance for doubtful accounts			18.4
Additional allowances deemed	0	0	0	0
Domestic Country [Member]
Income Tax Examination [Line Items]
Income taxes paid			49.0	254.5
Foreign Country [Member]
Income Tax Examination [Line Items]
Income taxes paid, net			96.5	76.2
State and Local Jurisdiction [Member]
Income Tax Examination [Line Items]
Income taxes paid, net			$ 0.2	$ 0.1