Principal Accounting Policies Book Overdrafts (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Accounting Policies [Abstract]
Book overdrafts	$ 28.8cnw_BookOverdrafts	$ 40.8cnw_BookOverdrafts

Book overdrafts represent outstanding drafts not yet presented to the bank that are in excess of recorded cash (as opposed to Bank overdrafts, which are checks presented to the bank that are in excess of cash on account at the bank).

No definition available.

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