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Debt And Other Financing Arrangements LT Debt terms (Details)
 12 Months Ended
Dec. 31, 2014
6.70% Senior Debentures Due 2034 [Member]  
Maturity year 2034
Effective interest rate 6.90%us-gaap_DebtInstrumentInterestRateEffectivePercentage
/ us-gaap_DebtInstrumentAxis
= cnw_SixPointSevenZeroPercentSeniorDebenturesDueTwoThousandThirtyFourMember
6.70% Senior Debentures Due 2034 [Member] | Minimum [Member]  
Redemption period of senior notes 30cnw_RedemptionPeriodOfSeniorNotes
/ us-gaap_DebtInstrumentAxis
= cnw_SixPointSevenZeroPercentSeniorDebenturesDueTwoThousandThirtyFourMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
6.70% Senior Debentures Due 2034 [Member] | Maximum [Member]  
Redemption period of senior notes 60cnw_RedemptionPeriodOfSeniorNotes
/ us-gaap_DebtInstrumentAxis
= cnw_SixPointSevenZeroPercentSeniorDebenturesDueTwoThousandThirtyFourMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
7.25% Senior Notes Due 2018 [Member]  
Maturity year 2018
Effective interest rate 7.37%us-gaap_DebtInstrumentInterestRateEffectivePercentage
/ us-gaap_DebtInstrumentAxis
= cnw_SevenPointTwoFivePercentSeniorNotesDueTwoThousandEighteenMember
7.25% Senior Notes Due 2018 [Member] | Minimum [Member]  
Redemption period of senior notes 30cnw_RedemptionPeriodOfSeniorNotes
/ us-gaap_DebtInstrumentAxis
= cnw_SevenPointTwoFivePercentSeniorNotesDueTwoThousandEighteenMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
7.25% Senior Notes Due 2018 [Member] | Maximum [Member]  
Redemption period of senior notes 60cnw_RedemptionPeriodOfSeniorNotes
/ us-gaap_DebtInstrumentAxis
= cnw_SevenPointTwoFivePercentSeniorNotesDueTwoThousandEighteenMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
2.63% Promissory Note Due 2016 [Member]  
Maturity year 2016
Effective interest rate 2.63%us-gaap_DebtInstrumentInterestRateEffectivePercentage
/ us-gaap_LongtermDebtTypeAxis
= cnw_PromissoryNote263Due2016Member