Capital Stock (Summary of Share Repurchases) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Equity, Class of Treasury Stock [Line Items]
Shares repurchased							3.9	5.0
Average price per share							$ 356.43	$ 269.15
Aggregate cost	$ 451	$ 480	$ 447	$ 758	$ 55	$ 529	$ 1,378	$ 1,342
Authorization remaining at the end of the period	$ 4,714			$ 2,450			$ 4,714	$ 2,450

Equity impact of the value of stock that has been repurchased and retired during the period. The excess of the purchase price over par value can be charged against retained earnings (once the excess is fully allocated to additional paid in capital).

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