Selected Quarterly Financial Results (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Net Sales	$ 2,601.0	$ 2,623.3	$ 2,584.7	$ 2,319.2	$ 2,479.3	$ 2,581.4	$ 2,412.1	$ 2,129.6	$ 10,128.2	$ 9,602.4	$ 8,801.2
Gross Profit	425.4	432.7	426.9	384.6	412.3	420.0	400.8	350.4	1,669.6	1,583.5	1,390.8
Income (loss) from operations	130.9	139.7	136.4	103.6	111.1	139.7	128.2	91.7	510.6	470.7	352.7
Net income (loss)	33.3	38.0	36.8	10.9	19.0	37.1	(34.8)	(4.2)	119.0	17.1	(29.2)
Corporate [Member]
Net Sales	1,442.8	1,312.8	1,394.4	1,362.8	1,386.4	1,330.3	1,338.4	1,279.3	5,512.8	5,334.4	4,833.6
Income (loss) from operations									349.0	331.6	256.2
Corporate [Member] | Medium/Large [Member]
Net Sales	1,178.5	1,055.7	1,124.7	1,089.6	1,118.6	1,070.6	1,075.0	1,022.9
Corporate [Member] | Small Business [Member]
Net Sales	264.3	257.1	269.7	273.2	267.8	259.7	263.4	256.4
Public [Member]
Net Sales	1,001.3	1,163.7	1,040.4	817.6	959.0	1,123.1	951.2	723.9	4,023.0	3,757.2	3,560.6
Income (loss) from operations									246.7	233.3	193.0
Public [Member] | Government [Member]
Net Sales	404.9	408.6	318.0	262.6	427.4	388.1	296.1	231.9
Public [Member] | Education [Member]
Net Sales	226.4	394.7	349.5	221.7	224.1	415.7	343.3	214.6
Public [Member] | Healthcare [Member]
Net Sales	370.0	360.4	372.9	333.3	307.5	319.3	311.8	277.4
Other [Member]
Net Sales	156.9	146.8	149.9	138.8	133.9	128.0	122.5	126.4	592.4	510.8	407.0
Income (loss) from operations									$ 18.6	$ 17.5	$ 14.3