Annual report pursuant to Section 13 and 15(d)

Reconciliation of Beginning and Ending Balances for Plan Assets Valued using Significant Unobservable Inputs (Detail)

v2.4.0.6
Reconciliation of Beginning and Ending Balances for Plan Assets Valued using Significant Unobservable Inputs (Detail) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2012
Private Equity
  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Balance at December 31, 2011 $ 33.0
Return on plan assets:  
Unrealized 1.0
Realized 1.6
Purchases 6.5
Sales (6.1)
Balance at December 31, 2012 36.0
Hedge Funds
  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Balance at December 31, 2011 92.9
Return on plan assets:  
Unrealized 4.7
Realized 1.0
Purchases 5.9
Sales (15.4)
Balance at December 31, 2012 89.1
Real Assets
  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Balance at December 31, 2011 9.8
Return on plan assets:  
Unrealized 0.6
Purchases 1.2
Sales (0.5)
Balance at December 31, 2012 $ 11.1