Financial Instruments - Total Short-Term and Long-Term Investments (Details) - USD ($) $ in Millions		Sep. 30, 2018	Dec. 31, 2017
Financial Instruments [Abstract]
Equity securities		$ 1,213	$ 2,150
Available-for-sale debt securities		11,256	15,362
Held-to-maturity debt securities		1,211	1,138
Total Short-term investments	[1]	13,680	18,650
Equity securities		1,563	1,440
Trading debt securities		50	73
Available-for-sale debt securities		3,742	5,090
Held-to-maturity debt securities		63	4
Private equity investments carried at equity-method or cost		1,027	408
Total Long-term investments	[1]	6,444	7,015
Held-to-maturity cash equivalents		$ 237	$ 719

[1] Amounts may not add due to rounding.