Capital Stock (Summary of Stock Option Activity) (Details) $ / shares in Units, shares in Millions, $ in Millions	9 Months Ended
	Sep. 30, 2015 USD ($) $ / shares shares
Number of Shares [Roll Forward]
Outstanding at beginning of period, Number of Shares	7.3
Granted, Number of Shares	1.3
Exercised, Number of Shares	(2.2)
Forfeited or expired, Number of Shares	(0.2)
Outstanding at end of period, Number of Shares	6.2
Exercisable at end of period, Number of Shares	4.0
Weighted-Average Option Price Per Share [Roll Forward]
Outstanding at beginning of period, Weighted-Average Option Price per Share | $ / shares	$ 70.30
Granted, Weighted-Average Option Price per Share | $ / shares	146.91
Exercised, Weighted-Average Option Price per Share | $ / shares	67.84
Forfeited or expired, Weighted-Average Option Price per Share | $ / shares	98.52
Outstanding at end of period, Weighted-Average Option Price per Share | $ / shares	86.60
Exercisable at end of period, Weighted-Average Option Price per Share | $ / shares	$ 71.60
Outstanding at end of period, Weighted-Average Remaining Contractual Life	4 years 6 months 15 days
Exercisable at end of period, Weighted-Average Remaining Contractual Life	3 years 29 days
Outstanding at end of period, Aggregate Intrinsic Value | $	$ 337.7
Exercisable at end of period, Aggregate Intrinsic Value | $	$ 275.0