Revenue (Schedule of New Accounting Pronouncements) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2018
Item Effected [Line Items]
Net sales	$ 1,816.7	$ 1,981.4	$ 1,948.0	$ 1,777.8	$ 1,862.2	$ 1,870.3	$ 1,832.3	$ 1,637.7	$ 7,523.9	$ 7,202.5	$ 6,631.2
Cost of merchandise sold									6,094.9	5,821.6	$ 5,369.9
Merchandise inventory	654.2				658.7				654.2	658.7
Other current assets	51.7				54.1				51.7	54.1
Other non-current liabilities	2.3				8.7				2.3	8.7
Retained Earnings	$ 694.0				678.1				$ 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					668.2
Other current assets					54.4					54.4
Other non-current liabilities					19.4					19.4
Retained Earnings					677.2					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)					(9.5)
Other current assets					(0.3)					(0.3)
Other non-current liabilities					(10.7)					(10.7)
Retained Earnings					$ 0.9					$ 0.9		$ 0.8