Net Income Per Share (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
Basic
Average common shares outstanding (in shares)									91,803,528	92,992,457	92,908,638
Continuing operations									$ 1,541.3	$ 1,108.7	$ 1,769.5
Discontinued operations											(41.6)
Net income	$ 248.6	$ 576.5	$ 471.0	$ 245.2	$ 101.0	$ 354.0	$ 403.6	$ 250.1	$ 1,541.3	$ 1,108.7	$ 1,727.9
Basic net income per share:
Continuing operations (in dollars per share)									$ 16.79	$ 11.92	$ 19.04
Discontinued operations (in dollars per share)											(0.44)
Net income per share - basic (in dollars per share)	$ 2.71	$ 6.28	$ 5.13	$ 2.67	$ 1.09	$ 3.80	$ 4.34	$ 2.68	$ 16.79	$ 11.92	$ 18.60
Diluted
Average common shares outstanding (in shares)									91,803,528	92,992,457	92,908,638
Stock options and other contingently issuable shares (in shares)									1,601,213	1,938,586	1,931,157
Non-vested restricted stock grants (in shares)									42,101	57,027	87,418
Average common shares outstanding assuming dilution (in shares)									93,446,842	94,988,070	94,927,213
Diluted net income per share:
Continuing operations (in dollars per share)									$ 16.49	$ 11.67	$ 18.64
Discontinued operations (in dollars per share)											(0.44)
Net income per share - diluted (in dollars per share)	$ 2.66	$ 6.16	$ 5.03	$ 2.62	$ 1.07	$ 3.72	$ 4.25	$ 2.62	$ 16.49	$ 11.67	$ 18.20
Net Income Per Common Share (Textual) [Abstract]
Anti-dilutive shares (in shares)									449,167	28,321	638,795