Stock Option Plans (Tables)

12 Months Ended

Dec. 31, 2020

Text Block [Abstract]

Black-Scholes Option Pricing Model with Weighted Average

For purposes of expense recognition in 2020, 2019 and 2018, the estimated fair values of the stock option grants are amortized to expense over the options’ vesting period.  We estimated the fair value of stock options at the date of grant using the Black-Scholes option pricing model with the following weighted average assumptions:

	Year Ended December 31,
	2020			2019			2018
Expected dividend yield		2.1	%		1.7	%		2.3	%
Expected risk-free interest rate		0.7	%		2.5	%		2.7	%
Volatility		17.3	%		15.6	%		15.1	%
Expected life (in years)		5.4			5.5			5.5

Stock Option Activity and Related Information

The following is a summary of our stock option activity and related information for 2020 and 2019 (in millions, except exercise price and year data):

						Weighted
						Average
				Weighted		Remaining
	Shares			Average		Contractual		Aggregate
	Under			Exercise		Term		Intrinsic
	Option			Price		(in years)		Value
Year Ended December 31, 2020
Beginning balance		7.9		$	56.40
Granted		1.6			86.17
Exercised		(1.8	)		45.80
Forfeited or canceled		(0.2	)		65.87
Ending balance		7.5		$	65.09		3.86	$	437.9
Exercisable at end of year		1.9		$	47.17		1.83	$	147.2
Ending unvested and expected to vest		5.3		$	70.74		4.51	$	278.1
Year Ended December 31, 2019
Beginning balance		8.8		$	50.16
Granted		1.3			79.59
Exercised		(1.9	)		42.91
Forfeited or canceled		(0.3	)		57.33
Ending balance		7.9		$	56.40		3.75	$	308.6
Exercisable at end of year		2.0		$	45.03		1.82	$	101.9
Ending unvested and expected to vest		5.7		$	59.76		4.36	$	201.5

Other Information Regarding Stock Options Outstanding and Exercisable

Other information regarding stock options outstanding and exercisable at December 31, 2020 is summarized as follows (in millions, except exercise price and year data):

					Options Outstanding						Options Exercisable
							Weighted
							Average
							Remaining		Weighted				Weighted
							Contractual		Average				Average
					Number		Term		Exercise		Number		Exercise
Range of Exercise Prices					Outstanding		(in years)		Price		Exercisable		Price
$	43.71	—	$	43.71		1.4		2.21	$	43.71		0.7	$	43.71
	46.17	—		46.87		0.9		0.97		46.33		0.9		46.33
	49.55	—		56.86		1.3		3.21		56.83		0.3		56.81
	70.74	—		70.74		1.1		4.21		70.74		—		70.74
	79.59	—		79.59		1.2		5.20		79.59		—		79.59
	86.17	—		86.17		1.6		6.20		86.17		—		—
$	43.71	—	$	86.17		7.5		3.86	$	65.09		1.9	$	47.17