Consolidated Statements Of Cash Flows (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash flows from operating activities:
Net income (loss)	$ 244.9	$ 132.8	$ 119.0
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation and amortization	207.9	208.2	210.2
Equity-based compensation expense	16.4	46.6	22.1
Deferred income taxes	(89.1)	(48.7)	(56.3)
Allowance for doubtful accounts	0.3	0	0
Amortization of deferred financing costs	6.4	8.8	13.6
Net (loss) gain on extinguishments of long-term debt	90.7	64.0	17.2
Income (Loss) from Equity Method Investments	(1.2)	0	0
Other Operating Activities, Cash Flow Statement	0.5	1.7	1.0
Changes in assets and liabilities:
Accounts receivable	(117.6)	(170.8)	(10.4)
Merchandise inventory	44.2	(67.5)	7.1
Other assets	(18.7)	(10.1)	(3.8)
Increase (Decrease) in Accounts Payable, Trade	43.7	146.1	0.8
Other current liabilities	1.7	64.1	(2.1)
Long-term liabilities	4.9	(8.9)	(1.0)
Net cash provided by operating activities	435.0	366.3	317.4
Cash flows from investing activities:
Capital expenditures	(55.0)	(47.1)	(41.4)
Payments to Acquire Equity Method Investments	(86.8)	0	0
Payment of accrued charitable contribution related to the MPK Coworker Incentive Plan II	(20.9)	0	0
Premium payments on interest rate cap agreements	(2.1)	0	(0.3)
Net cash used in investing activities	(164.8)	(47.1)	(41.7)
Cash flows from financing activities:
Proceeds from borrowings under revolving credit facility	0	63.0	289.0
Repayments of borrowings under revolving credit facility	0	(63.0)	(289.0)
Repayments of long-term debt	(15.4)	(51.1)	(201.0)
Proceeds from issuance of long-term debt	1,175.0	1,535.2	135.7
Payments to extinguish long-term debt	(1,299.0)	(2,047.4)	(243.2)
Payments of debt financing costs	(21.9)	(6.1)	(2.1)
Investment from CDW Holdings LLC	0	0	2.8
Net change in accounts payable-inventory financing	75.5	7.4	(29.5)
Net proceeds from issuance of common shares	0	424.7	0
Proceeds from Stock Options Exercised	1.3	0	0
Proceeds from Coworker Stock Purchase Plan	5.8	0	0
Dividends paid	(33.6)	(7.3)	0
Excess Tax Benefit from Share-based Compensation, Financing Activities	0.3	0.6	0
Payment of incentive compensation plan withholding taxes	0	(24.1)	0
Repurchase of common shares	0	(0.2)	(0.7)
Net cash used in financing activities	(112.0)	(168.3)	(338.0)
Effect of exchange rate changes on cash and cash equivalents	(1.8)	(0.7)	0.3
Net increase (decrease) in cash and cash equivalents	156.4	150.2	(62.0)
Cash and cash equivalents - beginning of period	188.1	37.9	99.9
Cash and cash equivalents - end of period	344.5	188.1	37.9
Supplementary disclosure of cash flow information:
Interest paid, including cash settlements on interest rate swap agreements	(195.8)	(267.6)	(302.7)
Taxes refunded (paid), net	(241.2)	(82.5)	(123.2)
Non-cash investing and financing activities:
Capital expenditures accrued in accounts payable-trade	$ 0.6	$ 0.2	$ 0.5