Capital Stock (Summary of Stock Option Activity) (Details) $ / shares in Units, shares in Millions, $ in Millions	9 Months Ended
	Sep. 30, 2016 USD ($) $ / shares shares
Number of Shares [Roll Forward]
Outstanding at beginning of period, Number of Shares | shares	6.0
Granted, Number of Shares | shares	1.4
Exercised, Number of Shares | shares	(1.2)
Forfeited or expired, Number of Shares | shares	(0.3)
Outstanding at end of period, Number of Shares | shares	5.9
Exercisable at end of period, Number of Shares | shares	4.0
Weighted-Average Option Price Per Share [Roll Forward]
Outstanding at beginning of period, Weighted-Average Option Price per Share | $ / shares	$ 87.23
Granted, Weighted-Average Option Price per Share | $ / shares	131.89
Exercised, Weighted-Average Option Price per Share | $ / shares	61.23
Forfeited or expired, Weighted-Average Option Price per Share | $ / shares	116.81
Outstanding at end of period, Weighted-Average Option Price per Share | $ / shares	101.68
Exercisable at end of period, Weighted-Average Option Price per Share | $ / shares	$ 87.16
Outstanding at end of period, Weighted-Average Remaining Contractual Life	5 years 3 months 7 days
Exercisable at end of period, Weighted-Average Remaining Contractual Life	3 years 8 months 23 days
Outstanding at end of period, Aggregate Intrinsic Value | $	$ 174.3
Exercisable at end of period, Aggregate Intrinsic Value | $	$ 165.7