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Pensions and Other Postretirement Benefits - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Level 1 And Level 2 [Member]
     
Pension And Other Employee Benefit Plans [Line Items]      
CMRT asset mix 83.00% 83.00%  
Defined benefit pension plans [Member]
     
Pension And Other Employee Benefit Plans [Line Items]      
Unamortized actuarial losses $ 16.5    
Prior service cost 1.2    
Average annual rate of return 14.00%    
Long term rate of return for plan assets 10.00% 10.00% 10.00%
Percentage of aggregate assets value 35.00%    
OPEB [Member]
     
Pension And Other Employee Benefit Plans [Line Items]      
Unamortized actuarial losses 7.5    
Prior service cost 16.2    
Defined contribution pension plans [Member]
     
Pension And Other Employee Benefit Plans [Line Items]      
Expenses related to pension plans 2.8 2.5 2.2
TIMET [Member]
     
Pension And Other Employee Benefit Plans [Line Items]      
Aggregate proceeds of total asset value $ 254.7