Commitments and Contingencies (Details 2) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012 item	Dec. 31, 2011	Dec. 31, 2010
Operating leases, future minimum payments due:
Total as of balance sheet date	$ 165.4
Due 2013	39.7
Due 2014	29.4
Due 2015	19.1
Due 2016	14.2
Due 2017	8.6
Due after 2017	54.4
Operating lease rentals for drilling contractors, office locations, warehouse buildings and some equipment	47.3	76.9	97.4
Sublease rental
Subleased space of previous corporate headquarters building (in number of floors)	3
Total subleases future lease payments	28.3
Subleases payments due 2013	2.2
Subleases payments due 2014	2.2
Subleases payments due 2015	2.2
Subleases payments due 2016	2.2
Subleases payments due 2017	2.2
Subleases payments due after 2017	$ 17.3

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Contractually required future rental payments receivable on noncancelable subleasing arrangements due in the year following the balance sheet date.

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Contractually required future rental payments receivable on noncancelable subleasing arrangements due within the fifth year following the balance sheet date.

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Contractually required future rental payments receivable on noncancelable subleasing arrangements due within the fourth year following the balance sheet date.

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Contractually required future rental payments receivable on noncancelable subleasing arrangements due within the third year following the balance sheet date.

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Contractually required future rental payments receivable on noncancelable subleasing arrangements due within the second year following the balance sheet date.

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Contractually required future rental payments receivable on noncancelable subleasing arrangements due after the fifth year following the balance sheet date.

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The amount of space subleased by the entity, expressed in number of floors.

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Amount of required minimum rental payments for leases having an initial or remaining non-cancelable letter-terms in excess of one year.

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Amount of required minimum rental payments maturing in the next fiscal year following the latest fiscal year for operating leases having an initial or remaining non-cancelable letter-terms in excess of one year.

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Amount of required minimum rental payments maturing in the forth fiscal year following the latest fiscal year for operating leases having an initial or remaining non-cancelable letter-terms in excess of one year.

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