Segment and Geographic Information - Geographic Reporting Segments Table (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012
Net sales: [Abstract]
Net sales	$ 2,620.7		$ 2,314.9		$ 7,276.3		$ 6,702.9
Income (loss) before income taxes: [Abstract]
Income (loss) before income taxes	18.9		16.9		42.8		39.7
Interest expense: [Abstract]
Interest expense	0.6		0.4		2.1		1.6
Depreciation and amortization: [Abstract]
Depreciation and amortization	6.8		6.3		20.2		19.0
Reportable Geographical Components [Member] | United States [Member]
Net sales: [Abstract]
Net sales	2,316.3		1,995.6		6,440.6		5,798.5
Income (loss) before income taxes: [Abstract]
Income (loss) before income taxes	14.9		10.3		36.8		29.3
Interest expense: [Abstract]
Interest expense	7.5		6.6		22.0		20.0
Depreciation and amortization: [Abstract]
Depreciation and amortization	5.1		4.4		15.0		13.1
Reportable Geographical Components [Member] | Canada [Member]
Net sales: [Abstract]
Net sales	298.5		311.2		812.1		881.0
Income (loss) before income taxes: [Abstract]
Income (loss) before income taxes	0.6		0.7		0.5		1.6
Interest expense: [Abstract]
Interest expense	0.1		0.1		0.5		0.5
Depreciation and amortization: [Abstract]
Depreciation and amortization	0.6		0.7		2.0		2.2
Corporate [Member]
Net sales: [Abstract]
Net sales	5.9	[1]	8.1	[1]	23.6	[1]	23.4	[1]
Income (loss) before income taxes: [Abstract]
Income (loss) before income taxes	3.4	[2]	5.9	[2]	5.5	[2]	8.8	[2]
Interest expense: [Abstract]
Interest expense	(7.0)	[2]	(6.3)	[2]	(20.4)	[2]	(18.9)	[2]
Depreciation and amortization: [Abstract]
Depreciation and amortization	$ 1.1	[2]	$ 1.2	[2]	$ 3.2	[2]	$ 3.7	[2]

[1] Consists primarily of external sales made by our consolidating warehouses, 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. and Canada, intercompany eliminations for interest and allocations of overhead, and LIFO income or expense.