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Financial Instruments - Information on Available-for-sale Investments (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Debt securities, amortized cost	$ 4,076		$ 4,076		$ 7,340
Debt securities, unrealized gains	50		50		6
Debt securities, unrealized losses	(3)		(3)		(85)
Debt securities, fair value	4,123		4,123		7,261
Publicly traded equity securities, fair value	756		756		456
Total debt and publicly traded equity securities, fair value	4,879		4,879		7,717
Unrealized net gain	(39)	$ 7	75	$ 50
Corporate notes and bonds
Debt Securities, Available-for-sale [Line Items]
Debt securities, amortized cost	2,666		2,666		4,985
Debt securities, unrealized gains	36		36		3
Debt securities, unrealized losses	(2)		(2)		(68)
Debt securities, fair value	2,700		2,700		4,920
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Debt securities, amortized cost	789		789		1,285
Debt securities, unrealized gains	4		4		1
Debt securities, unrealized losses	(1)		(1)		(11)
Debt securities, fair value	792		792		1,275
U.S. government and agency securities
Debt Securities, Available-for-sale [Line Items]
Debt securities, amortized cost	575		575		895
Debt securities, unrealized gains	10		10		2
Debt securities, unrealized losses	0		0		(5)
Debt securities, fair value	585		585		892
Foreign government bonds
Debt Securities, Available-for-sale [Line Items]
Debt securities, amortized cost	41		41		167
Debt securities, unrealized gains	0		0		0
Debt securities, unrealized losses	0		0		(1)
Debt securities, fair value	41		41		166
Mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Debt securities, amortized cost	5		5		8
Debt securities, unrealized gains	0		0		0
Debt securities, unrealized losses	0		0		0
Debt securities, fair value	$ 5		$ 5		$ 8

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Debt Securities and Equity Securities, FV-NI

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Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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