Stock Plans (Tables)

12 Months Ended

Dec. 31, 2020

Share-based Payment Arrangement [Abstract]

Summary of Stock Option and RSA Activity

A summary of stock option and RSU activity as of December 31, 2020, and corresponding changes during the year, are as follows:

	Stock Options			Service-Based RSUs			Service and Performance-Based RSUs
(Shares in thousands)	Shares	Weighted-Average Exercise Price		Shares	Weighted- Average Grant Price		Shares	Weighted- Average Grant Price
Outstanding as of December 31, 2019	4,172	$	72.70	2,412	$	91.42	3,392	$	88.25
Granted	422	131.68		816	127.56		1,089	122.15
Exercised/vested	(822)	53.50		(1,042)	82.77		(1,193)	78.52
Forfeited	(21)	65.43		(108)	105.32		(142)	101.38
Expired	—	—		—	—		—	—
Outstanding as of December 31, 2020	3,751	83.59		2,078	$	109.23	3,146	$	103.08
Options vested and expected to vest as of December 31, 2020	3,751	83.59
Options exercisable as of December 31, 2020	2,706	$	72.26

Weighted-average Remaining Contractual Life and Aggregate Intrinsic Value of the Company's Stock Options Outstanding, Exerciseable, and Vested and Expected to Vest

The weighted-average remaining contractual life and the aggregate intrinsic value (the amount by which the fair value of our stock price exceeds the exercise price of the option) of the stock options outstanding, exercisable, and vested and expected to vest as of December 31, 2020, were as follows:

	Outstanding		Exercisable		Vested and Expected to Vest
Weighted-average remaining contractual life (in years)	5.3		4.2		5.3
Aggregate intrinsic value (millions)	$	145	$	132	$	145

Weighted Average Assumptions Used

The fair value of each option is estimated on the date of grant using a Black-Scholes-Merton option-pricing model. The following weighted-average assumptions were used for options granted in 2020, 2019 and 2018:

	2020			2019			2018
Dividend yield	1.4		%	1.5		%	1.4		%
Expected volatility(a)	20		%	24		%	22		%
Risk-free interest rate	1.6		%	2.6		%	2.7		%
Expected life of stock option (in years)(b)	7.1			7.1			7.1
Weighted-average fair value per option	$	25.83		$	23.38		$	23.17

(a)The expected volatility is based on both weighted historical and implied volatilities of our common stock price.

(b)The expected life of stock options was determined using both historical data and expectations of option exercise behavior.

Schedule of Share-based Payment Award, Valuation Assumptions

The fair value of RSUs that do not include the r-TSR modifier, including those that contain only service conditions, is measured using our stock price on the grant date. The fair value of service and performance-based RSUs that include the r-TSR modifier is determined using a Monte Carlo valuation model with the following weighted-average assumptions for December 31:

	2020		2019
Expected volatility(a)	19	%	20	%
Risk-free interest rate	1.4	%	2.5	%
Remaining performance period (in years)	2.9		2.9

(a)The expected volatility is based on historical volatility of our common stock price.