Statements of Consolidated Income (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Statement [Abstract]
Revenue	$ 5,806,069us-gaap_Revenues	$ 5,473,356us-gaap_Revenues	$ 5,580,247us-gaap_Revenues
Salaries, wages and employee benefits	2,261,304us-gaap_LaborAndRelatedExpense	2,143,036us-gaap_LaborAndRelatedExpense	2,125,104us-gaap_LaborAndRelatedExpense
Purchased transportation	1,437,418cnw_PurchasedTransportation	1,323,005cnw_PurchasedTransportation	1,531,319cnw_PurchasedTransportation
Other operating expenses	649,154us-gaap_OtherCostAndExpenseOperating	634,107us-gaap_OtherCostAndExpenseOperating	567,810us-gaap_OtherCostAndExpenseOperating
Fuel and fuel-related taxes	498,604us-gaap_FuelCosts	532,958us-gaap_FuelCosts	553,301us-gaap_FuelCosts
Depreciation and amortization	242,658us-gaap_DepreciationAndAmortization	230,751us-gaap_DepreciationAndAmortization	216,215us-gaap_DepreciationAndAmortization
Purchased labor	174,061cnw_PurchasedLabor	148,165cnw_PurchasedLabor	113,619cnw_PurchasedLabor
Rents and leases	139,428us-gaap_LeaseAndRentalExpense	129,325us-gaap_LeaseAndRentalExpense	115,954us-gaap_LeaseAndRentalExpense
Maintenance	134,992us-gaap_MaintenanceCosts	123,056us-gaap_MaintenanceCosts	128,084us-gaap_MaintenanceCosts
Costs and Expenses	5,537,619us-gaap_OperatingExpenses	5,264,403us-gaap_OperatingExpenses	5,351,406us-gaap_OperatingExpenses
Operating Income (Loss)	268,450us-gaap_OperatingIncomeLoss	208,953us-gaap_OperatingIncomeLoss	228,841us-gaap_OperatingIncomeLoss
Investment income	686us-gaap_InvestmentIncomeNet	621us-gaap_InvestmentIncomeNet	831us-gaap_InvestmentIncomeNet
Interest expense	(53,456)us-gaap_InterestExpense	(53,339)us-gaap_InterestExpense	(54,777)us-gaap_InterestExpense
Miscellaneous, net	(4,983)us-gaap_OtherNonoperatingExpense	(1,870)us-gaap_OtherNonoperatingExpense	(3,941)us-gaap_OtherNonoperatingExpense
Other Nonoperating Income (Expense)	(57,753)us-gaap_NonoperatingIncomeExpense	(54,588)us-gaap_NonoperatingIncomeExpense	(57,887)us-gaap_NonoperatingIncomeExpense
Income before income tax provision	210,697	154,365	170,954
Income Tax Provision (Benefit)	73,658us-gaap_IncomeTaxExpenseBenefit	55,212us-gaap_IncomeTaxExpenseBenefit	66,408us-gaap_IncomeTaxExpenseBenefit
Net Income	$ 137,039us-gaap_NetIncomeLoss	$ 99,153us-gaap_NetIncomeLoss	$ 104,546us-gaap_NetIncomeLoss
Weighted Average Common Shares Outstanding, Basic	57,390,945	56,511,563	55,837,574
Weighted Average Common Shares Outstanding, Diluted	58,018,443	57,240,588	56,485,987
Earnings Per Common Share, Basic	$ 2.39us-gaap_EarningsPerShareBasic	$ 1.75us-gaap_EarningsPerShareBasic	$ 1.87us-gaap_EarningsPerShareBasic
Earnings Per Common Share, Diluted	$ 2.36us-gaap_EarningsPerShareDiluted	$ 1.73us-gaap_EarningsPerShareDiluted	$ 1.85us-gaap_EarningsPerShareDiluted
Cash Dividends Declared per Common Share	$ 0.50	$ 0.40	$ 0.40

Costs incurred for temporary contract labor.

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Costs incurred with outside service providers for the transportation of customer shipments.

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Aggregate dividends declared during the period for each share of common stock outstanding.

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Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Amount of the cost of borrowed funds accounted for as interest expense.

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