Stock-based compensation (Tables)

12 Months Ended

Dec. 31, 2021

Share-based Payment Arrangement [Abstract]

Components of stock-based compensation expense recognized in the Consolidated Statements of Income

The following table reflects the components of stock-based compensation expense recognized in our Consolidated Statements of Income (in millions):

	Years ended December 31,
	2021		2020		2019
RSUs	$	183	$	178	$	168
Performance units	121		118		105
Stock options	37		34		35
Total stock-based compensation expense, pretax	341		330		308
Tax benefit from stock-based compensation expense	(74)		(72)		(67)
Total stock-based compensation expense, net of tax	$	267	$	258	$	241

Summary of RSUs

The following table summarizes information regarding our RSUs:

	Year ended December 31, 2021
	Units (in millions)	Weighted-average grant date fair value
Balance nonvested as of December 31, 2020	3.0	$	198.11
Granted	1.3	$	233.10
Vested	(0.9)	$	177.27
Forfeited	(0.4)	$	213.32
Balance nonvested as of December 31, 2021	3.0	$	217.95

Weighted-average assumptions used and the resulting weighted-average grant date fair value of stock options

The weighted-average assumptions used in the option valuation model and the resulting weighted-average grant date fair values of stock options granted were as follows:

	Years ended December 31,
	2021			2020			2019
Closing price of our common stock on grant date	$	237.17		$	236.36		$	177.31
Expected volatility (average of implied and historical volatility)	25.6		%	28.1		%	23.5		%
Expected life (in years)	5.7			5.8			5.8
Risk-free interest rate	1.0		%	0.4		%	2.4		%
Expected dividend yield	2.9		%	3.0		%	3.1		%
Fair value of stock options granted	$	40.43		$	42.34		$	30.47

Summary of stock options

The following table summarizes information regarding our stock options:

	Year ended December 31, 2021
	Options (in millions)	Weighted- average exercise price		Weighted- average remaining contractual life (in years)	Aggregate intrinsic value (in millions)
Balance unexercised as of December 31, 2020	4.7	$	179.90
Granted	1.3	$	237.17
Exercised	(0.5)	$	137.95
Expired/forfeited	(0.4)	$	208.56
Balance unexercised as of December 31, 2021	5.1	$	197.27	7.3	$	168
Vested or expected to vest as of December 31, 2021	4.9	$	195.64	7.2	$	167
Exercisable as of December 31, 2021	2.0	$	165.46	5.6	$	120

Weighted average assumptions used and the resulting weighted average grant date fair value of performance units

The weighted-average assumptions used in the payout simulation model and the resulting weighted-average grant date fair values of performance units granted were as follows:

	Years ended December 31,
	2021			2020			2019
Closing price of our common stock on grant date	$	239.64		$	236.36		$	177.31
Volatility	29.3		%	27.5		%	22.1		%
Risk-free interest rate	0.3		%	0.2		%	2.3		%
Fair value of units granted	$	254.68		$	249.07		$	188.40