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, 2020 USD ($) $ / shares shares
Shares (in thousands)
Options - beginning balance (in shares) | shares	36,185
Granted (in shares) | shares	4,976
Exercised (in shares) | shares	(13,019)
Forfeited or expired (in shares) | shares	(601)
Options - ending balance (in shares) | shares	27,541
Options exercisable (in shares) | shares	18,084
Weighted Average Exercise Price
Options - beginning of period (in dollars per share) | $ / shares	$ 69
Options - shares granted (in dollars per share) | $ / shares	76
Options - shares exercised (in dollars per share) | $ / shares	67
Options - shares forfeited or expired (in dollars per share) | $ / shares	72
Options - end of period (in dollars per share) | $ / shares	72
Options exercisable - end of period (in dollars per share) | $ / shares	$ 70
Weighted average remaining contractual life, options outstanding (in years)	4 years
Weighted average remaining contractual life, options exercisable (in years)	3 years
Intrinsic value of unexercised in-the-money options, options outstanding | $	$ 386
Intrinsic value of unexercised in-the-money options, options exercisable | $	$ 274