Common Equity (Tables)

12 Months Ended

Dec. 31, 2019

Stockholders' Equity Note [Abstract]

Schedule of stock-based compensation expense and related deferred tax benefit recognized in income

The following table summarizes our pre-tax stock-based compensation expense and the related tax benefit recognized in income for the years ended December 31:

(in millions)	2019		2018		2017
Stock options	$	4.4	$	5.2	$	3.4
Restricted stock	7.1		10.7		5.4
Performance units	38.7		20.2		20.2
Stock-based compensation expense	$	50.2	$	36.1	$	29.0
Related tax benefit	$	13.8	$	9.9	$	11.6

Schedule of stock option activity

The following is a summary of our stock option activity during 2019:

Stock Options	Number of Options		Weighted-Average Exercise Price		Weighted-Average Remaining Contractual Life (in years)	Aggregate Intrinsic Value (in millions)
Outstanding as of January 1, 2019	4,452,533		$	48.86
Granted	476,418		$	68.18
Exercised	(1,609,948	)	$	41.63
Forfeited	(69,085	)	$	62.33
Outstanding as of December 31, 2019	3,249,918		$	54.98	6.3	$	121.0
Exercisable as of December 31, 2019	1,744,386		$	46.92	4.8	$	79.0

Schedule of restricted stock activity

The following restricted stock activity occurred during 2019:

Restricted Shares	Number of Shares		Weighted-Average Grant Date Fair Value
Outstanding and unvested as of January 1, 2019	234,627		$	61.01
Granted	97,343		$	68.18
Released	(192,291	)	$	60.76
Forfeited	(5,570	)	$	62.99
Outstanding and unvested as of December 31, 2019	134,109		$	66.48

Schedule of shares repurchased

The following is a summary of shares purchased to fulfill exercised stock options and restricted stock awards during the years ended December 31:

(in millions)	2019		2018		2017
Shares purchased	1.8		1.1		1.1
Cost of shares purchased	$	140.1	$	72.4	$	71.3

Schedule of dividends declared

During the year ended December 31, 2019, our Board of Directors declared common stock dividends which are summarized below:

Date Declared	Date Payable	Per Share	Period
January 17, 2019	March 1, 2019	$0.59	First quarter
April 18, 2019	June 1, 2019	$0.59	Second quarter
July 18, 2019	September 1, 2019	$0.59	Third quarter
October 17, 2019	December 1, 2019	$0.59	Fourth quarter