Share-Based Compensation Plans (Details 3) shares in Thousands	12 Months Ended
	Dec. 31, 2017 $ / shares shares
Time-Vested
Summary of Nonvested stock awards
Nonvested stock outstanding at January 1 (in shares) | shares	476
Granted (in shares) | shares	117
Vested (in shares) | shares	(141)
Forfeited (in shares) | shares	(19)
Nonvested stock outstanding at December 31 (in shares) | shares	433
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Nonvested stock outstanding at January 1, Weighted-Average Grant Date Fair Value (in dollars per share) | $ / shares	$ 67.31
Granted, weighted-Average grant date fair value (in dollars per share) | $ / shares	75.61
Vested,Weighted-Average Grant Date Fair Value (in dollars per share) | $ / shares	78.18
Forfeited, Weighted-Average Grant Date Fair Value (in dollars per share) | $ / shares	69.95
Nonvested stock outstanding at December 31, Weighted-Average Grant Date Fair Value (in dollars per share) | $ / shares	$ 65.91
Market-Based
Summary of Nonvested stock awards
Nonvested stock outstanding at January 1 (in shares) | shares	66
Granted (in shares) | shares	45
Vested (in shares) | shares	(15)
Forfeited (in shares) | shares	(4)
Nonvested stock outstanding at December 31 (in shares) | shares	92
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Nonvested stock outstanding at January 1, Weighted-Average Grant Date Fair Value (in dollars per share) | $ / shares	$ 64.33
Granted, weighted-Average grant date fair value (in dollars per share) | $ / shares	73.43
Vested,Weighted-Average Grant Date Fair Value (in dollars per share) | $ / shares	61.07
Forfeited, Weighted-Average Grant Date Fair Value (in dollars per share) | $ / shares	81.47
Nonvested stock outstanding at December 31, Weighted-Average Grant Date Fair Value (in dollars per share) | $ / shares	$ 68.26
Performance-Based
Summary of Nonvested stock awards
Nonvested stock outstanding at January 1 (in shares) | shares	72
Granted (in shares) | shares	79
Vested (in shares) | shares	(30)
Forfeited (in shares) | shares	(27)
Nonvested stock outstanding at December 31 (in shares) | shares	94
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Nonvested stock outstanding at January 1, Weighted-Average Grant Date Fair Value (in dollars per share) | $ / shares	$ 70.92
Granted, weighted-Average grant date fair value (in dollars per share) | $ / shares	76.47
Vested,Weighted-Average Grant Date Fair Value (in dollars per share) | $ / shares	75.62
Forfeited, Weighted-Average Grant Date Fair Value (in dollars per share) | $ / shares	48.71
Nonvested stock outstanding at December 31, Weighted-Average Grant Date Fair Value (in dollars per share) | $ / shares	$ 78.91