STOCK-BASED COMPENSATION.

SHARES AUTHORIZED FOR STOCK-BASED COMPENSATION PROGRAMS.

At December 31, 2017, a total of 39,301,717 shares of unissued common stock were authorized for issuance under our stock-based compensation plans. Additionally, a total of 2,693,679 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 2017.



	Options		Weighted- average exercise price		Weighted-average remaining contractual term in years
Outstanding at December 31, 2016	24,364,322		$	61.90
Exercised	(8,977,164	)	$	53.04
Forfeited	(126,404	)	$	75.16
Expired	(39,631	)	$	76.06
Outstanding at December 31, 2017	15,221,123		$	66.98	5.1
Exercisable at December 31, 2017	11,140,190		$	63.79	4.5

Compensation and related costs includes a charge for stock option-based compensation expense of $63.7 million in 2015, $44.9 million in 2016, and $28.1 million in 2017.

The total intrinsic value of options exercised was $108.1 million in 2015, $150.5 million in 2016, and $293.0 million in 2017. At December 31, 2017, the aggregate intrinsic value of in-the-money options outstanding was $577.6 million, including $458.3 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 2017.



	Restricted shares		Restricted stock units		Weighted- average fair value
Nonvested at December 31, 2016	931,508		4,634,461		$	72.19
Time-based grants	17,022		2,026,176		$	100.24
Performance-based grants	—		114,454		$	101.79
Vested (value at vest date was $164.5 million)	(455,958	)	(1,111,857	)	$	71.77
Forfeited	(19,457	)	(106,323	)	$	72.32
Nonvested at December 31, 2017	473,115		5,556,911		$	82.37

Nonvested at December 31, 2017, includes 7,200 performance-based restricted shares and 407,808 performance-based restricted stock units. These nonvested performance-based restricted shares and units include 7,200 shares and 293,354 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 $85.3 million in 2015, $116.7 million in 2016, and $124.0 million in 2017.

At December 31, 2017, non-employee directors held 78,286 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 (in millions) to be recognized over the remaining vesting periods of the stock-based awards outstanding at December 31, 2017. Estimated future compensation expense will change to reflect future grants changes in the probability of performance thresholds being met, and adjustments for actual forfeitures.



First quarter 2018	$	47.3
Second quarter 2018	46.7
Third quarter 2018	46.0
Fourth quarter 2018	40.3
Total 2018	180.3
2019 through 2023	176.1
Total	$	356.4