Capital Stock (Summary of Stock Option Activity) (Details) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2022 USD ($) $ / shares shares
Number of Shares [Roll Forward]
Outstanding at beginning of period, Number of Shares | shares	2.9
Granted, Number of Shares | shares	0.5
Exercised, Number of Shares | shares	(0.2)
Forfeited or expired, Number of Shares | shares	0.0
Outstanding at end of period, Number of Shares | shares	3.2
Exercisable at end of period, Number of Shares | shares	1.9
Weighted-Average Option Price Per Share [Roll Forward]
Outstanding at beginning of period, Weighted-Average Option Price per Share | $ / shares	$ 255.50
Granted, Weighted-Average Option Price per Share | $ / shares	451.50
Exercised, Weighted-Average Option Price per Share | $ / shares	249.89
Forfeited or expired, Weighted-Average Option Price per Share | $ / shares	306.80
Outstanding at end of period, Weighted-Average Option Price per Share | $ / shares	288.98
Exercisable at end of period, Weighted-Average Option Price per Share | $ / shares	$ 238.19
Outstanding at end of period, Weighted-Average Remaining Contractual Life	7 years 21 days
Exercisable at end of period, Weighted-Average Remaining Contractual Life	5 years 10 months 13 days
Outstanding at end of period, Aggregate Intrinsic Value | $	$ 643
Exercisable at end of period, Aggregate Intrinsic Value | $	$ 480