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Earnings Per Share - Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share (Detail) (Forward equity [Member])
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2013
May 2013, Contract [Member]
  
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]  
Forward equity agreements contract date May 2013
Forward equity agreements settlement date September and October 2013
Forward Equity Agreement Entered, not included in computation of diluted EPS prior to the date of settlement 39.1
January 2012, Contract [Member]
  
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]  
Forward equity agreements contract date January 2012
Forward equity agreements settlement date June 2012
Forward Equity Agreement Entered, not included in computation of diluted EPS prior to the date of settlement 19.0
March 2011, Contract [Member]
  
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]  
Forward equity agreements contract date March 2011
Forward equity agreements settlement date April 2011
Forward Equity Agreement Entered, not included in computation of diluted EPS prior to the date of settlement 9.5