Quarterly report pursuant to Section 13 or 15(d)

Asset Impairment - Additional Information (Detail)

v2.4.0.6
Asset Impairment - Additional Information (Detail) (U.S. Drilling Segment [Member], USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2011
U.S. Drilling Segment [Member]
 
Operating Statistics [Line Items]  
Non-cash pre-tax impairment charge $ 170.0
Asset Impairment charge after tax $ 109.1