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Segment Reporting Narrative (Details) (USD $)
In Thousands, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Number of operating segments 3us-gaap_NumberOfOperatingSegments    
Unallocated [Member]      
Defined Benefit Plan, Net Periodic Benefit Cost 13,500us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost
/ us-gaap_NatureOfExpenseAxis
= cnw_UnallocatedMember		 $ 4,200us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost
/ us-gaap_NatureOfExpenseAxis
= cnw_UnallocatedMember		  
Allocated [Member]      
Defined Benefit Plan, Net Periodic Benefit Cost     $ 9,600us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost
/ us-gaap_NatureOfExpenseAxis
= cnw_AllocatedMember