Revenue (Schedule of New Accounting Pronouncements) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Item Effected [Line Items]
Net sales	$ 1,851.6	$ 1,877.9	$ 1,763.0	$ 1,773.2	$ 1,816.7	$ 1,981.4	$ 1,948.0	$ 1,777.8	$ 7,265.7	$ 7,523.9	$ 7,202.5
Cost of merchandise sold									5,896.2	6,094.9	5,821.6
Merchandise inventory	588.5				654.2				588.5	654.2	658.7
Other current assets	56.6				51.7				56.6	51.7	54.1
Other non-current liabilities	4.7				2.3				4.7	2.3	8.7
Retained Earnings	$ 725.1				$ 694.0				$ 725.1	$ 694.0	678.1
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Item Effected [Line Items]
Net sales											7,202.3
Cost of merchandise sold											5,821.6
Merchandise inventory											668.2
Other current assets											54.4
Other non-current liabilities											19.4
Retained Earnings											677.2
Accounting Standards Update 2014-09 [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Item Effected [Line Items]
Net sales											0.2
Merchandise inventory											(9.5)
Other current assets											(0.3)
Other non-current liabilities											(10.7)
Retained Earnings											$ 0.9