Supplemental Financial Information (Details Textual) (USD $) In Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2010	Dec. 31, 2009
Income Tax Examination [Line Items]
Amount of bad debts recorded in prior periods and subsequently recovered	$ 1.0	$ 2.0	$ 11.1	$ 5.9
Supplemental financial information (Textual) [Abstract]
Interest paid on long-term debt			54.0	54.6
First installment of new drillship due					154.4
Interest on Internal Revenue Service Assessment				0.9
Unpaid accrued capital expenditures			11.9		28.9	64.9
Domestic Country [Member]
Income Tax Examination [Line Items]
Income taxes paid			64.0	362.5
Foreign Country [Member]
Income Tax Examination [Line Items]
Income taxes paid, net			121.9	88.5
State and Local Jurisdiction [Member]
Income Tax Examination [Line Items]
Income taxes paid, net			0.2	1.0
Egypt Customers [Member]
Income Tax Examination [Line Items]
Amount of bad debts recorded in prior periods and subsequently recovered			2.6	4.9
Additional allowances deemed	5.7	0	5.7	0
North Sea Customer [Member]
Income Tax Examination [Line Items]
Amount of bad debts recorded in prior periods and subsequently recovered			8.5	1.0
Amount of trade accounts receivable written off against allowance for doubtful accounts			$ 18.4