9. Share-based Compensation (Tables)

12 Months Ended

Dec. 31, 2015

Stock Options

The following table summarizes stock option activity:



	Shares		Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value (in millions)
Outstanding, January 1, 2013	747,293		$	70.83
Granted	55,050		$	117.67
Exercised	(159,450	)	$	54.16
Forfeited/expired	(13,250	)	$	91.32
Outstanding, December 31, 2013	629,643		$	78.72
Granted	54,000		$	119.71
Exercised	(91,387	)	$	63.66
Forfeited/expired	(10,450	)	$	100.29
Outstanding, December 31, 2014	581,806		$	84.50
Granted	40,500		$	139.56
Exercised	(195,221	)	$	61.29
Forfeited/expired	(380	)	$	62.47
Outstanding, December 31, 2015	426,705		$	100.36	5.46	$	16.4
Vested and expected to vest,
December 31, 2015	417,883		$	99.75	5.41	$	16.3
Exercisable, December 31, 2015	282,895		$	89.43	4.23	$	13.9

Stock Options Valuation Assumptions

The weighted-average fair value of stock options granted was estimated using a Black-Scholes option-pricing model with the following weighted-average assumptions:



	Year Ended December 31,
	2015			2014			2013
Expected volatility	23		%	25		%	28		%
Risk-free interest rate	1.90		%	2.35		%	2.65		%
Expected life (in years)	7.7			8.7			8.9
Expected dividend	—			—			—
Weighted-average fair value of options granted	$	42.74		$	43.96		$	47.25

Resticted Stock Activity

The following table summarizes restricted stock and restricted stock unit activity:



	Restricted Stock & Restricted Stock Units		Weighted- Average Grant-Date Fair Value		Weighted-Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value (in millions)
Outstanding, January 1, 2013	361,458		$	96.15
Granted	144,445		$	117.09
Vested	(104,883	)	$	91.76
Forfeited	(25,590	)	$	95.97
Outstanding, December 31, 2013	375,430		$	105.44
Granted	145,695		$	119.56
Vested	(107,557	)	$	98.52
Forfeited	(36,203	)	$	108.17
Outstanding, December 31, 2014	377,365		$	112.60
Granted	177,110		$	139.56
Vested	(113,347	)	$	107.62
Forfeited	(28,706	)	$	116.19
Outstanding, December 31, 2015	412,422		$	125.30	2.16	$	57.2

Employee Stock Purchase Plan, Valuation Assumptions

The fair value of the employees’ purchase rights under the 2011 ESPP and the 1988 ESPP was estimated using a Black-Scholes model with the following weighted-average assumptions:



	Year Ended December 31,
	2015			2014			2013
Expected volatility	18		%	15		%	19		%
Risk-free interest rate	0.02		%	0.04		%	0.05		%
Expected life (in years)	0.25			0.25			0.25
Expected dividend	—			—			—
Weighted-average fair value
of purchase rights	$	25.08		$	21.88		$	21.76