12. Stock-Based Compensation Plans

As of March 31, 2016, we have the 2014 Stock Incentive Plan, the Employee Stock Purchase Plan, the 2014 Directors Stock Plan, the Long-Term Performance Plan, the Amended and Restated 2010 Stock Incentive Plan, the 2005 Directors Stock Plan, the Stock Incentive Plan and the Directors Stock Plan (“Stock Based Compensation Plans”). As of May 20, 2014, no new grants will be made under the Amended and Restated 2010 Stock Incentive Plan or the 2005 Directors Stock Plan. No grants have been made under the Stock Incentive Plan, the Directors Stock Plan or the Long-Term Performance Plan since at least 2005. Under the terms of the 2014 Stock Incentive Plan, grants may be nonqualified stock options, incentive stock options qualifying under Section 422 of the Internal Revenue Code, restricted stock, restricted stock units, stock appreciation rights, performance shares, performance units or other stock-based awards. The 2014 Directors Stock Plan provides for the grant of nonqualified stock options, restricted stock, restricted stock units or other stock-based awards to our nonemployee directors. To date, we have not granted any incentive stock options, restricted stock or performance units under any plans.

As of March 31, 2016, the maximum number of new shares of common stock that were available for grant under the 2014 Stock Incentive Plan and the 2014 Directors Stock Plan was 10.0 million.

For awards with graded vesting, we use an accelerated expense attribution method. The compensation cost that was charged against income for stock-based awards granted under the Stock-Based Compensation Plans was as follows:

	For the three months ended March 31,
	2016		2015
	(in millions)
Compensation cost	$	17.9	$	18.4
Related income tax benefit	5.5		6.0
Capitalized as part of an asset	0.6		0.7

Nonqualified Stock Options

Nonqualified stock options were granted to certain employees under the 2014 Stock Incentive Plan. Total options granted were 1.1 million for the three months ended March 31, 2016. The fair value of stock options is estimated using the Black-Scholes option pricing model. The following is a summary of the assumptions used in this model for the stock options granted during the period:

	For the three months ended
	March 31, 2016
Expected volatility	31.7		%
Expected term (in years)	6.5
Risk-free interest rate	1.5		%
Expected dividend yield	4.07		%
Weighted average estimated fair value per common share	$	8.91

As of March 31, 2016, we had $10.2 million of total unrecognized compensation cost related to nonvested stock options. The cost is expected to be recognized over a weighted-average service period of approximately 1.7 years.

Performance Share Awards

Performance share awards were granted to certain employees under the 2014 Stock Incentive Plan. Total performance share awards granted were 0.3 million for the three months ended March 31, 2016. The performance share awards granted represent initial target awards and do not reflect potential increases or decreases resulting from the final performance results to be determined at the end of the performance period. The actual number of common shares to be awarded at the end of each performance period will range between 0% and 150% of the initial target awards. The fair value of performance share awards is determined based on the closing stock price of our common shares on the grant date. The weighted-average grant date fair value of these performance share awards granted was $37.38 per common share.

As of March 31, 2016, we had $14.3 million of total unrecognized compensation cost related to nonvested performance share awards granted. The cost is expected to be recognized over a weighted-average service period of approximately 1.8 years.

Restricted Stock Units

Restricted stock units were issued to certain employees and agents pursuant to the 2014 Stock Incentive Plan and non-employee directors pursuant to the 2015 Directors Stock Plan. Total restricted stock units granted were 1.2 million for the three months ended March 31, 2016. The fair value of restricted stock units is determined based on the closing stock price of our common shares on the grant date. The weighted-average grant date fair value of these restricted stock units granted was $37.39 per common share.

As of March 31, 2016, we had $77.0 million of total unrecognized compensation cost related to nonvested restricted stock unit awards granted. The cost is expected to be recognized over a weighted-average period of approximately 2.1 years.