Capital Stock (Share Repurchases) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Equity, Class of Treasury Stock [Line Items]
Shares repurchased	9.4	6.3
Average price per share	$ 286.35	$ 268.65
Aggregate cost	$ 2,700	$ 1,701	$ 1,685
Authorization remaining at the end of each period	$ 1,092	$ 3,792

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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