STOCK-BASED COMPENSATION.

SHARES AUTHORIZED FOR STOCK-BASED COMPENSATION PROGRAMS.

At December 31, 2018, a total of 37,976,738 shares of unissued common stock were authorized for issuance under our stock-based compensation plans. Additionally, a total of 2,340,343 shares are authorized for issuance under a plan whereby substantially all employees may acquire common stock through payroll deductions at prevailing market prices.

STOCK OPTIONS.

The following table summarizes the status of, and changes in, our stock options during 2018.



	Options		Weighted- average exercise price		Weighted-average remaining contractual term in years
Outstanding at December 31, 2017	15,221,123		$	66.98
Exercised	(3,831,062	)	$	60.68
Forfeited	(73,416	)	$	76.08
Expired	(16,252	)	$	71.99
Outstanding at December 31, 2018	11,300,393		$	69.05	4.5
Exercisable at December 31, 2018	9,251,542		$	67.39	4.1

Compensation and related costs includes a charge for stock option-based compensation expense of $15.3 million in 2018, $28.1 million in 2017, and $44.9 million in 2016.

The total intrinsic value of options exercised was $208.4 million in 2018, $293.0 million in 2017, and $150.5 million in 2016. At December 31, 2018, the aggregate intrinsic value of in-the-money options outstanding was $262.9 million, including $230.6 million related to options exercisable.

RESTRICTED SHARES AND STOCK UNITS.

The following table summarizes the status of, and changes in, our nonvested restricted shares and restricted stock units during 2018.



	Restricted shares		Restricted stock units		Weighted- average fair value
Nonvested at December 31, 2017	473,115		5,556,911		$	82.37
Time-based grants	8,775		2,438,198		$	92.37
Performance-based grants	—		160,821		$	92.03
Vested (value at vest date was $160.9 million)	(330,920	)	(1,412,089	)	$	79.32
Forfeited	(14,006	)	(139,921	)	$	79.74
Nonvested at December 31, 2018	136,964		6,603,920		$	87.07

Nonvested at December 31, 2018 includes 2,400 performance-based restricted shares and 473,615 performance-based restricted stock units. These nonvested performance-based restricted shares and units include 2,400 shares and 198,340 units for which the performance period has lapsed and the performance threshold has been met.

Compensation and related costs includes expenses for restricted shares and restricted stock units of $181.8 million in 2018, $124.0 million in 2017, and $116.7 million in 2016.

At December 31, 2018, non-employee directors held 47,639 vested stock units that will convert to common shares upon their separation from the Board.

FUTURE STOCK-BASED COMPENSATION EXPENSE.

The following table presents the compensation expense to be recognized over the remaining vesting periods of the stock-based awards outstanding at December 31, 2018. Estimated future compensation expense will change to reflect future grants, changes in the probability of performance thresholds being met, and adjustments for actual forfeitures.



(in millions)
First quarter 2019	$	51.4
Second quarter 2019	50.6
Third quarter 2019	50.5
Fourth quarter 2019	45.2
Total 2019	197.7
2020 through 2024	188.6
Total	$	386.3