Capital Stock (Summary of Stock Option Activity) (Details) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
Mar. 31, 2020 USD ($) $ / shares shares
Number of Shares [Roll Forward]
Outstanding at beginning of period, Number of Shares \| shares	3.1
Granted, Number of Shares \| shares	1.0
Exercised, Number of Shares \| shares	(0.3)
Forfeited or expired, Number of Shares \| shares	0.0
Outstanding at end of period, Number of Shares \| shares	3.8
Exercisable at end of period, Number of Shares \| shares	2.2
Weighted-Average Option Price Per Share [Roll Forward]
Outstanding at beginning of period, Weighted-Average Option Price per Share \| $ / shares	$ 190.31
Granted, Weighted-Average Option Price per Share \| $ / shares	271.27
Exercised, Weighted-Average Option Price per Share \| $ / shares	107.46
Forfeited or expired, Weighted-Average Option Price per Share \| $ / shares	256.05
Outstanding at end of period, Weighted-Average Option Price per Share \| $ / shares	216.40
Exercisable at end of period, Weighted-Average Option Price per Share \| $ / shares	$ 171.44
Outstanding at end of period, Weighted-Average Remaining Contractual Life	7 years 1 month 24 days
Exercisable at end of period, Weighted-Average Remaining Contractual Life	5 years 6 months 25 days
Outstanding at end of period, Aggregate Intrinsic Value \| $	$ 139
Exercisable at end of period, Aggregate Intrinsic Value \| $	$ 139

The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.