Segment and Geographic Information - Geographic Reporting Segments Table (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2014		Jun. 30, 2013		Jun. 30, 2014		Jun. 30, 2013
Net sales:
Net sales	$ 2,623.2		$ 2,509.9		$ 4,924.1		$ 4,655.6
Income (loss) before income taxes:
Income (loss) before income taxes	19.9		19.8		23.9		23.9
Interest expense:
Interest expense	0.6		0.8		1.3		1.5
Depreciation and amortization:
Depreciation and amortization	7.9		6.8		15.1		13.4
Reportable Geographical Components [Member] | United States
Net sales:
Net sales	2,294.3		2,218.7		4,333.4		4,124.3
Income (loss) before income taxes:
Income (loss) before income taxes	19.8		18.2		23.0		21.9
Interest expense:
Interest expense	7.8		7.5		15.3		14.4
Depreciation and amortization:
Depreciation and amortization	6.2		4.9		11.7		9.8
Reportable Geographical Components [Member] | Canada
Net sales:
Net sales	319.9		281.3		575.9		513.5
Income (loss) before income taxes:
Income (loss) before income taxes	0.7		0.2		0.4		(0.1)
Interest expense:
Interest expense	0.1		0.1		0.4		0.4
Depreciation and amortization:
Depreciation and amortization	0.7		0.7		1.4		1.4
Corporate [Member]
Net sales:
Net sales	9.0	[1]	9.9	[1]	14.8	[1]	17.8	[1]
Income (loss) before income taxes:
Income (loss) before income taxes	(0.6)	[2]	1.4	[2]	0.5	[2]	2.1	[2]
Interest expense:
Interest expense	(7.3)	[2]	(6.8)	[2]	(14.4)	[2]	(13.3)	[2]
Depreciation and amortization:
Depreciation and amortization	$ 1.0	[2]	$ 1.2	[2]	$ 2.0	[2]	$ 2.2	[2]

[1] Consists primarily of external sales made by the Company's consolidating warehouse, management service fee revenue, an allowance for sales returns and certain other sales adjustments..

[2] Consists primarily of net expenses and other income that is not allocated to the U.S. or Canada, intercompany eliminations for interest and allocations of overhead, and LIFO expense.