Capital Stock (Summary of Share Repurchases) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Equity, Class of Treasury Stock [Line Items]
Shares repurchased							5.0	5.2
Average price per share							$ 269.15	$ 270.42
Aggregate cost	$ 758	$ 55	$ 529	$ 644	$ 458	$ 294	$ 1,342	$ 1,396
Authorization remaining at the end of the period	$ 2,450			$ 4,098			$ 2,450	$ 4,098