Consolidated Statement Of Shareholders' (Deficit) Equity (USD $) In Millions, except Share data	Total	Paid-In Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Preferred Stock [Member]	Common Stock [Member]
Balance at at Dec. 31, 2011	$ (7.3)	$ 2,184.7	$ (2,191.3)	$ (2.1)	$ 0	$ 1.4
Preferred Stock, Shares Issued at Dec. 31, 2011					0
Common Stock, Shares, Issued at Dec. 31, 2011						144,900,000
Equity-based compensation expense	22.1	22.1	0	0	0	0
Investment from CDW Holdings LLC	2.8	2.8	0	0	0	0
Repurchase of Class B Common Shares	(0.7)	0	(0.7)	0	0	0
Treasury Stock, Shares, Acquired						0
Accrued charitable contribution related to the MPK Coworker Incentive Plan II, net of tax	(1.4)	(1.4)	0	0	0	0
Stock Issued During Period, Shares, Accrued Charitable Contribution related to the MPK Coworker Incentive Plan II						300,000
MPK Coworker Incentive Plan II units withheld for taxes	(0.5)	(0.5)	0	0	0	0
Net income (loss)	119.0	0	119.0	0	0	0
Foreign currency translation adjustment	2.5	0	0	2.5	0	0
Balance at at Dec. 31, 2012	136.5	2,207.7	(2,073.0)	0.4	0	1.4
Preferred Stock, Shares Issued at Dec. 31, 2012					0
Common Stock, Shares, Issued at Dec. 31, 2012						145,200,000
Equity-based compensation expense		46.6	0	0	0	0
Adjustments to Additional Paid in Capital, Share-based Compensation, Stock Options, Requisite Service Period Recognition	46.6
Stock Issued During Period, Value, New Issues	424.7	424.4	0	0	0	0.3
Stock Issued During Period, Shares, New Issues						26,800,000
Repurchase of Class B Common Shares	(0.2)	0	(0.2)	0	0	0
Dividends, Common Stock	(7.3)	0	(7.3)		0	0
Reclassification to goodwill for accrued charitable contributions	9.4	9.4	0	0	0	0
MPK Coworker Incentive Plan II units withheld for taxes	(24.1)	0	(24.1)	0	0	0
Stock Issued During Period, Shares, Incentive Compensation Plan units withheld for taxes						0
Net income (loss)	132.8	0	132.8	0	0	0
Foreign currency translation adjustment	(6.7)	0	0	(6.7)	0	0
Balance at at Dec. 31, 2013	711.7	2,688.1	(1,971.8)	(6.3)	0	1.7
Preferred Stock, Shares Issued at Dec. 31, 2013	0				0
Common Stock, Shares, Issued at Dec. 31, 2013	172,000,000					172,000,000
Equity-based compensation expense	16.4	16.4	0	0	0	0
Stock Issued During Period, Value, Stock Options Exercised	1.3	1.3	0	0	0	0
Adjustments to Additional Paid in Capital, Income Tax Benefit from Share-based Compensation	0.3	0.3	0	0	0	0
Stock Issued During Period, Shares, Employee Stock Purchase Plans						200,000
Stock Issued During Period, Value, Employee Stock Purchase Plan	(5.8)	(5.8)	0	0	0	0
Dividends, Common Stock	(33.6)	0	(33.6)	0	0	0
Net income (loss)	244.9	0	244.9	0	0	0
Foreign currency translation adjustment	(10.3)	0	0	(10.3)	0	0
Balance at at Dec. 31, 2014	$ 936.5	$ 2,711.9	$ (1,760.5)	$ (16.6)	$ 0	$ 1.7
Preferred Stock, Shares Issued at Dec. 31, 2014	0				0
Common Stock, Shares, Issued at Dec. 31, 2014	172,200,000					172,200,000