Share-Based Compensation (Summary of PSU Activity) (Details) - PSUs	9 Months Ended
	Sep. 30, 2017 $ / shares shares
One Year Performance Share Unit Program
Number of Awards
Number of Awards, Unvested balances at beginning of period (in shares) | shares	378,766
Number of Awards, Granted (in shares) | shares	197,075
Number of Awards, Vested (in shares) | shares	(10,729)
Number of Awards, Forfeited (in shares) | shares	(41,063)
Number of Awards, Unvested balances at end of period (in shares) | shares	524,049
Weighted-Average Grant Date Fair Value
Weighted-Average Grant Date Fair Value, Unvested balances at beginning of period (in dollars per share) | $ / shares	$ 52.55
Weighted-Average Grant Date Fair Value, Granted (in dollars per share) | $ / shares	65.51
Weighted-Average Grant Date Fair Value, Vested (in dollars per share) | $ / shares	53.72
Weighted-Average Grant Date Fair Value, Forfeited (in dollars per share) | $ / shares	55.95
Weighted-Average Grant Date Fair Value, Unvested balances at end of period (in dollars per share) | $ / shares	$ 57.13
Three Year Performance Share Unit Program
Number of Awards
Number of Awards, Unvested balances at beginning of period (in shares) | shares	1,314,668
Number of Awards, Granted (in shares) | shares	803,712
Number of Awards, Vested (in shares) | shares	(1,079,925)
Number of Awards, Forfeited (in shares) | shares	(28,497)
Number of Awards, Unvested balances at end of period (in shares) | shares	1,009,958
Weighted-Average Grant Date Fair Value
Weighted-Average Grant Date Fair Value, Unvested balances at beginning of period (in dollars per share) | $ / shares	$ 63.18
Weighted-Average Grant Date Fair Value, Granted (in dollars per share) | $ / shares	55.57
Weighted-Average Grant Date Fair Value, Vested (in dollars per share) | $ / shares	42.83
Weighted-Average Grant Date Fair Value, Forfeited (in dollars per share) | $ / shares	87.86
Weighted-Average Grant Date Fair Value, Unvested balances at end of period (in dollars per share) | $ / shares	$ 78.18