Commitments And Contingencies (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012
Specific customer allowance for uncollectible trade accounts receivable gross unpaid amounts	$ 6.1
Specific customer allowance for uncollectible trade accounts receivable allowance recorded	$ 2.3

Allowancefordoubtfulaccountsreceivablespecificcustomerallowancerecorded

No definition available.

Name:	cnw_Allowancefordoubtfulaccountsreceivablespecificcustomerallowancerecorded
Namespace Prefix:	cnw_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant