Financial Instruments (Carrying Amount of Equity Securities) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Total sale price	$ 909	$ 240
Total initial cost	261	120
Cumulative net gains	648	$ 120
Total initial cost, marketable securities	1,865		$ 1,935
Cumulative net gain, marketable securities	949		1,361
Carrying value, marketable securities	2,814		3,296
Total initial cost, non-marketable securities	8,777		8,297
Cumulative net gain, non-marketable securities	2,006		3,056
Carrying value, non-marketable securities	10,783		11,353
Total initial cost	10,642		10,232
Cumulative net gain	2,955		4,417
Carrying value	13,597		14,649
Cumulative net gain of non-marketable securities	3,800		3,500
Cumulative unrealized loss of non-marketable securities	$ 1,700		$ 445