Equity Incentive Plan (Tables)

12 Months Ended

Dec. 31, 2019

Share-based Payment Arrangement [Abstract]

Table of Performance Share Unit Monte Carlo Assumptions [Table Text Block]

	2019		2018		2017
Risk-free interest rate	1.69	%	3.03	%	1.73	%
Expected life in years	3		3		3
Expected volatility	24	%	26	%	28	%
Expected dividend yield	—		—		—

Schedule of Stock Options, Activity

	Number of Options		Weighted Average Exercise Price	Aggregate Intrinsic Value (in millions)
Outstanding at December 31, 2018	847,830		$260.88	$264.0
Granted	42,676		720.81
Exercised	(280,383	)	169.70
Forfeited	(1,408	)	661.92
Outstanding at December 31, 2019	608,715		334.20	279.5
Options exercisable at December 31, 2019	458,803		$259.02	$245.1

Schedule Shares Outstanding under Stock Option Plans, by Exercise Price Range

Number of Options Outstanding	Weighted Average Exercise Price	Remaining Contractual Life of Options Outstanding	Options Exercisable
184,729	$158.97	2.3	184,729
145,927	$254.61	4.4	145,927
153,226	$354.45	6.3	100,952
124,833	$661.68	8.9	27,195
608,715		5.2	458,803

Schedule of Stock Options, Valuation Assumptions

	2019		2018		2017
Risk-free interest rate	1.74	%	3.09	%	2.00	%
Expected life in years	6.0		5.9		5.8
Expected volatility	24	%	26	%	28	%
Expected dividend yield	—		—		—

Schedule Restricted Stock Units, Activity

	Number of Restricted Stock Units		Aggregate Intrinsic Value (in millions)	Number of Performance Share Units		Aggregate Intrinsic Value (in millions)
Outstanding at December 31, 2018	49,252		$27.8	12,814		$7.2
Granted	11,750			4,505
Vested	(16,948	)		—
Forfeited	(3,069	)		(136	)
Outstanding at December 31, 2019	40,985		$32.5	17,183		$13.6