NET INCOME PER SHARE (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Basic
Net income	$ 705.8	$ 595.9	$ 321.7	$ 576.5	$ 471.0	$ 245.2	$ 1,623.4	$ 1,292.7
Average shares outstanding (in shares)	90,537,314			91,823,573			90,694,317	91,850,565
Basic net income per share (in dollars per share)	$ 7.80			$ 6.28			$ 17.90	$ 14.07
Diluted
Net income	$ 705.8	$ 595.9	$ 321.7	$ 576.5	$ 471.0	$ 245.2	$ 1,623.4	$ 1,292.7
Average shares outstanding assuming dilution:
Average shares outstanding (in shares)	90,537,314			91,823,573			90,694,317	91,850,565
Stock options and other contingently issuable shares (in shares)	1,561,994			1,742,298			1,546,419	1,611,078
Non-vested restricted stock grants (in shares)	10,921			38,389			17,052	48,461
Average shares outstanding assuming dilution (in shares)	92,110,229			93,604,260			92,257,788	93,510,104
Diluted net income per share (in dollars per share)	$ 7.66			$ 6.16			$ 17.60	$ 13.82
Stock options and other contingently issuable shares with anti-dilutive effects (in shares)	0			0			63,753	9,853