Note 12 - Equity Compensation Plans (Tables)

9 Months Ended

Sep. 30, 2020

Notes Tables

Share-based Payment Arrangement, Option, Activity [Table Text Block]

	Stock Option							Restricted Stock					PSU
	Number of Options			Weighted Average Exercise Price		Aggregate Intrinsic Value		Number of Shares			Weighted Average Grant Date Fair Value Per Share		Number of Shares			Weighted Average Grant Date Fair Value Per Share
						(in millions)
Outstanding at December 31, 2019		6,432,814		$	79.51	$	449.2		428,729		$	107.96		93,960		$	158.50
Granted		924,810		$	158.94				159,328		$	159.30		50,736		$	192.93
Dividend reinvestment		—		$	—				—		$	—		713			N/A
Exercised or lapsed		(1,308,469	)	$	54.86	$	148.4		(169,101	)	$	99.91		—
Canceled, expired or forfeited		(114,597	)	$	123.00				(20,341	)	$	121.60		—
Outstanding at September 30, 2020		5,934,558		$	96.48	$	527.2		398,615		$	130.77		145,409		$	170.75
Exercisable at September 30, 2020		3,799,648		$	75.69	$	416.5
Exercisable at December 31, 2019		4,175,855		$	65.05	$	352.0
Nonvested at September 30, 2020		2,134,910							398,615					145,409
Expected to vest at September 30, 2020		1,880,444							351,554					269,001	(1)

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]

	2020		2019
Option pricing model	Black-Scholes		Black-Scholes
Expected volatility	18.41	%	18.76	%
Risk-free interest rate	1.53	%	2.27	%
Expected term in years	4.3		4.4
Dividend yield	0.71	%	0.80	%
Weighted average grant date fair value per stock option	$25.77		$24.09