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Quarterly Financial Data Narrative (Details) (USD $)
In Millions, unless otherwise specified
 3 Months Ended
Dec. 31, 2014
Jun. 30, 2014
Jun. 30, 2013
Quarterly Financial Data [Line Items]      
Quarterly Financial Information, Quarterly Charges and Credits, Amount Affecting Comparability $ 5.4us-gaap_QuarterlyFinancialInformationQuarterlyChargesAndCreditsAmountAffectingComparability    
Freight      
Quarterly Financial Data [Line Items]      
Quarterly Financial Information, Quarterly Charges and Credits, Amount Affecting Comparability   3.4us-gaap_QuarterlyFinancialInformationQuarterlyChargesAndCreditsAmountAffectingComparability
/ us-gaap_StatementBusinessSegmentsAxis
= cnw_FreightMember		  
Corporate and Eliminations [Member]      
Quarterly Financial Data [Line Items]      
Quarterly Financial Information, Quarterly Charges and Credits, Amount Affecting Comparability 16.0us-gaap_QuarterlyFinancialInformationQuarterlyChargesAndCreditsAmountAffectingComparability
/ us-gaap_StatementBusinessSegmentsAxis
= cnw_CorporateandEliminationsMember		   5.6us-gaap_QuarterlyFinancialInformationQuarterlyChargesAndCreditsAmountAffectingComparability
/ us-gaap_StatementBusinessSegmentsAxis
= cnw_CorporateandEliminationsMember
Logistics      
Quarterly Financial Data [Line Items]      
Quarterly Financial Information, Quarterly Charges and Credits, Amount Affecting Comparability     $ 3.7us-gaap_QuarterlyFinancialInformationQuarterlyChargesAndCreditsAmountAffectingComparability
/ us-gaap_StatementBusinessSegmentsAxis
= cnw_LogisticsMember