Capital Stock and Stock-Based Compensation Plans - Summary of Stock Option Activity (Details) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($) $ / shares shares
Summary of stock option plan activity [Roll Forward]
Options - beginning balance (in shares) | shares	40,979
Granted (in shares) | shares	6,290
Exercised (in shares) | shares	(6,669)
Forfeited or expired (in shares) | shares	(890)
Options - ending balance (in shares) | shares	39,710
Options exercisable (in shares) | shares	26,420
Additional disclosures pertaining to stock options [Abstract]
Weighted average exercise price of options - beginning of period (in dollars per share) | $ / shares	$ 65
Weighted average exercise price of options - shares granted (in dollars per share) | $ / shares	68
Weighted average exercise price of options - shares exercised (in dollars per share) | $ / shares	55
Weighted average exercise price of options - shares forfeited or expired (in dollars per share) | $ / shares	71
Weighted average exercise price of options - end of period (in dollars per share) | $ / shares	67
Weighted average exercise price of options exercisable - end of period (in dollars per share) | $ / shares	$ 66
Weighted average remaining contractual life, options outstanding (in years)	3 years
Weighted average remaining contractual life, options exercisable (in years)	3 years
Value of unexercised in-the-money options, options outstanding | $	$ 1,457
Value of unexercised in-the-money options, options exercisable | $	$ 1,457