Stock Compensation Plans (Tables)

12 Months Ended

Dec. 31, 2017

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Summary of significant stock options granted

The fair value of stock option awards granted during 2017, 2016 and 2015 was estimated at the date of grant using a Black-Scholes option-pricing method with the following assumptions:

	2017			2016			2015
Weighted-average fair value per option	$	10.60		$	6.49		$	11.67
Risk-free interest rate	1.96		%	1.22		%	1.58		%
Dividend yield	2.96		%	3.04		%	2.29		%
Expected stock volatility	32.25		%	34.12		%	36.53		%
Expected life - years	5			5			5

Summary of stock option activity

A summary of stock option award activity for the year ended December 31, 2017 is presented below:

	Number of Shares		Weighted-average Exercise Price		Weighted-average Remaining Contractual Term	Aggregate Intrinsic Value (millions)
Outstanding - beginning of year	3,783,497		$	34.41
Granted - new awards	484,186		45.43
Exercised	(1,053,189	)	32.62
Canceled or expired	(63,373	)	36.94
Outstanding - end of year	3,151,121		$	36.65	6 years	$	39.4
Options expected to vest	3,151,121		$	36.65	6 years	$	39.4
Options exercisable	1,859,277		$	36.05	5 years	$	24.4

Summary of restricted share activity

A summary of stock award activity, including restricted shares, deferred shares, performance-based restricted stock units and time-based restricted stock units that will settle in common shares for the year ended December 31, 2017 is as follows:

	Number of Shares		Weighted-average Grant Date Fair Value
Outstanding - beginning of year	1,349,175		$	34.96
Granted - new awards	407,436		45.48
Vested	(445,036	)	37.18
Canceled or expired	(66,301	)	35.96
Outstanding - end of year	1,245,274		$	37.56