Financial Instruments (Carrying Amount of Equity Securities) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Debt and Equity Securities, FV-NI [Line Items]
Total sale price	$ 4,767	$ 3,134
Total initial cost	2,674	858
Cumulative net gains (losses)	2,093	2,276
Total initial cost, Marketable Equity Securities	2,227	1,935
Cumulative net gain (loss), Marketable Equity Securities	3,631	1,361
Carrying value, Marketable Equity Securities	5,858	3,296
Total initial cost, Non-Marketable Equity Securities	14,616	8,297
Cumulative net gain (loss), Non-Marketable Equity Securities	4,277	3,056
Carrying value, Non-Marketable Equity Securities	18,893	11,353
Total initial cost	16,843	10,232
Cumulative net gain (loss)	7,908	4,417
Carrying value	24,751	14,649
Cumulative net gain	6,100	3,500
Unrealized losses (including impairment)	1,900	$ 445
Other Noncurrent Assets
Debt and Equity Securities, FV-NI [Line Items]
Carrying value, Marketable Equity Securities	$ 429