Equity Incentive Plans (Tables)

12 Months Ended

Dec. 31, 2017

Equity Incentive Plans [Abstract]

Assumptions used to determine the fair value of options granted

Option grant assumptions
	2017		2016		2015
Weighted average expected term	6.1 years		5.0 years		6.5 years
Expected volatility	15.7 - 32.7%		16.0 - 34.3%		16.0 - 37.8%
Weighted average volatility	21.0	%	24.3	%	24.7	%
Expected dividends	1.4 - 1.9%		1.9 - 2.1%		1.6 - 2.1%
Weighted average expected dividends	1.9	%	2.1	%	1.7	%
Risk-free rate	0.5 - 2.5%		0.2 - 2.4%		0.0 - 2.4%

Summary of option activity

Summary of option activity
	For the year ended December 31, 2017
	Number (in 000s)		Weighted average exercise price		Aggregate intrinsic value (in 000s)		Weighted average remaining contractual term (years)
Outstanding as of January 1, 2017	13,560		$	50.01
Granted	2,631		78.93
Exercised	(4,688	)	44.91
Forfeited	(229	)	70.85
Expired	(12	)	59.91
Outstanding as of December 31, 2017	11,262		58.46		$	520,900	6.5
Outstanding, net of expected forfeitures	11,140		58.27		517,276		6.5
Outstanding, exercisable (“vested”)	6,314		47.83		359,121		5.1

Changes in restricted stock units

Changes in restricted stock units
	For the year ended December 31, 2017
	Number (in 000s)		Weighted average grant date fair value
Nonvested as of January 1, 2017	1,679		$	58.49
Granted	333		80.12
Vested	(718	)	51.42
Forfeited	(53	)	69.19
Nonvested as of December 31, 2017	1,241		67.93

Changes in performance stock units

Changes in performance stock awards
	For the year ended December 31, 2017
	Number (in 000s)		Weighted average grant date fair value
Nonvested as of January 1, 2017	919		$	61.50
Granted	458		78.47
Adjustment for performance achievement	(33	)	52.75
Vested	(213	)	52.52
Forfeited	(41	)	69.30
Nonvested as of December 31, 2017	1,090		70.35