Common Stock (Tables)

12 Months Ended

Dec. 31, 2017

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

Stock Options Status and Activity

The following table reflects the status and activity for all options to purchase common stock for the period indicated:

	Year Ended December 31, 2017
	Shares Under Option			Weighted Avg. Exercise Prices		Weighted Avg. Remaining Life in Years		Aggregate Intrinsic Value
								(Millions)
Outstanding Stock Options:
Outstanding, January 1, 2017		606,525		$	38.54		2.6	$	12
Canceled		(2,214	)		56.23
Forfeited		(1,107	)		56.23
Exercised		(164,863	)		33.70				5
Outstanding, March 31, 2017		438,341		$	40.22		2.6	$	11
Forfeited		(278	)		66.54
Exercised		(3,242	)		45.42				—
Outstanding, June 30, 2017		434,821		$	40.16		2.4	$	8
Forfeited		(41,369	)		19.53
Exercised		(50,125	)		34.79				1
Outstanding, September 30, 2017		343,327		$	43.44		2.4	$	4
Forfeited		(628	)		62.54
Exercised		(24,683	)		40.86				—
Outstanding, December 31, 2017		318,016		$	43.60		2.3	$	5

Nonvested Restricted Shares

The following table reflects the status for all nonvested restricted shares for the period indicated:

	Year Ended December 31, 2017
	Shares			Weighted Avg. Grant Date Fair Value
Nonvested Restricted Shares
Nonvested balance at January 1, 2017		591,416		$	44.63
Granted		182,543			68.04
Vested		(261,003	)		50.95
Forfeited		(65,354	)		53.12
Nonvested balance at March 31, 2017		447,602		$	49.25
Granted		23,295			57.22
Vested		(15,336	)		46.77
Forfeited		(6,271	)		48.10
Nonvested balance at June 30, 2017		449,290		$	49.79
Granted		2,001			55.80
Vested		(4,581	)		55.52
Forfeited		(10,234	)		44.82
Nonvested balance at September 30, 2017		436,476		$	49.87
Vested		(19,228	)		47.45
Forfeited		(6,997	)		51.79
Nonvested balance at December 31, 2017		410,251		$	49.95