Share Based Compensation Arrangement by Share Based Payment Award Equity Instruments Other than Options Expected to Vest (Detail) (USD $)	Jun. 30, 2011	Dec. 31, 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant Date Fair Value	$ 48.06	$ 43.25
Long Term Performance Plan 2009-2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected Number of Units to be Issued	550,394
Grant Date Fair Value	$ 27.77
Long Term Performance Plan 2010-2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected Number of Units to be Issued	203,900
Grant Date Fair Value	$ 78.18
Long Term Performance Plan 2011-2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected Number of Units to be Issued	82,010
Grant Date Fair Value	$ 109.35