Consolidated Statements Of Cash Flows (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Cash flows from operating activities:
Net income (loss)	$ 119.0	$ 17.1	$ (29.2)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation and amortization	210.2	204.9	209.4
Equity-based compensation expense	22.1	19.5	11.5
Deferred income taxes	(56.3)	(10.2)	(4.3)
Allowance for doubtful accounts	0	0.4	(1.3)
Amortization of deferred financing costs	13.6	15.7	18.0
Net loss (gain) on extinguishments of long-term debt	17.2	118.9	(2.0)
Realized loss on interest rate swap agreements	0	2.8	51.5
Mark to market loss on interest rate derivatives	0.9	4.2	4.7
Net loss (gain) on sale and disposals of assets	0.1	0.3	0.7
Other	0	(0.6)	(0.6)
Changes in assets and liabilities:
Accounts receivable	(8.6)	(165.3)	(81.5)
Merchandise inventory	7.1	(29.0)	(34.9)
Other assets	(3.8)	50.3	(61.9)
Accounts payable-trade	0.8	(19.8)	269.3
Other current liabilities	(3.9)	21.5	77.8
Long-term liabilities	(1.0)	(16.0)	(3.5)
Net cash provided by operating activities	317.4	214.7	423.7
Cash flows from investing activities:
Capital expenditures	(41.4)	(45.7)	(41.5)
Cash settlements on interest rate swap agreements	0	(6.6)	(78.2)
Premium payments on interest rate cap agreements	(0.3)	(3.7)	(5.9)
Proceeds from sale of assets and other	0	0	0.2
Net cash used in investing activities	(41.7)	(56.0)	(125.4)
Cash flows from financing activities:
Proceeds from borrowings under revolving credit facility	289.0	1,295.0	770.8
Repayments of borrowings under revolving credit facility	(289.0)	(1,483.2)	(1,074.1)
Repayments of long-term debt	(201.0)	(132.0)	(16.5)
Proceeds from issuance of long-term debt	135.7	1,175.0	500.0
Payments to extinguish long-term debt	(243.2)	(1,175.0)	(518.6)
Payments of debt financing costs	(2.1)	(26.3)	(14.3)
Investment from CDW Holdings LLC	2.8	1.0	0
Net change in accounts payable-inventory financing	(29.5)	250.5	3.2
Principal payments under capital lease obligations	0	0	(0.6)
Net cash used in financing activities	(338.0)	(95.4)	(350.1)
Effect of exchange rate changes on cash and cash equivalents	0.3	0	0.4
Net increase (decrease) in cash and cash equivalents	(62.0)	63.3	(51.4)
Cash and cash equivalents - beginning of period	99.9	36.6	88.0
Cash and cash equivalents - end of period	37.9	99.9	36.6
Supplementary disclosure of cash flow information:
Interest paid, including cash settlements on interest rate swap agreements	(302.7)	(332.9)	(377.0)
Taxes refunded (paid), net	(123.2)	20.9	(48.0)
Non-cash investing and financing activities:
Capital expenditures accrued in accounts payable-trade	0.5	1.1	0
Class B Common Shares [Member]
Cash flows from financing activities:
Repurchase of Class B common shares	$ (0.7)	$ (0.4)	$ 0