Selected Quarterly Financial Information (unaudited) (Quarterly Information) (Details) - USD ($) $ / shares in Units, $ 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
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 885.0	$ 1,032.9	$ 1,099.1	$ 790.3	$ 843.6	$ 1,030.2	$ 1,175.4	$ 834.8	$ 3,807.2	$ 3,883.9	$ 3,839.6
Gross Profit	247.8	298.3	332.1	201.6	224.5	301.9	361.6	223.2	1,079.8	1,111.2	1,125.2
Net Income (Loss)	$ 114.0	$ 114.7	$ 110.7	$ 69.3	$ 75.6	$ 108.0	$ 137.6	$ 37.9	$ 408.7	$ 359.0	$ 305.7
Basic Earnings (Loss) per Share (in usd per share)	$ 2.96	$ 2.97	$ 2.83	$ 1.75	$ 1.89	$ 2.68	$ 3.38	$ 0.91	$ 10.49	$ 8.84	$ 7.25
Diluted Earnings (Loss) per Share (in usd per share)	2.93	2.94	2.80	1.73	1.87	2.65	3.35	0.90	10.38	8.74	7.14
Cash Dividends per Common Share (in usd per share)	$ 0.77	$ 0.77	$ 0.77	$ 0.64	$ 0.64	$ 0.64	$ 0.64	$ 0.51	$ 2.95	$ 2.43	$ 1.96