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Financial Instruments - Information on Available-for-sale Investments (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Debt securities, fair value	$ 6,343		$ 7,261
Debt securities, amortized cost	6,338		7,340
Debt securities, unrealized gains	30		6
Debt securities, unrealized losses	(25)		(85)
Publicly traded equity securities, fair value	636		456
Total debt and publicly traded equity securities, fair value	6,979		7,717
Unrealized net gain	114	$ 44
Corporate notes and bonds
Debt Securities, Available-for-sale [Line Items]
Debt securities, fair value	4,310		4,920
Debt securities, amortized cost	4,307		4,985
Debt securities, unrealized gains	22		3
Debt securities, unrealized losses	(19)		(68)
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Debt securities, fair value	1,094		1,275
Debt securities, amortized cost	1,096		1,285
Debt securities, unrealized gains	3		1
Debt securities, unrealized losses	(5)		(11)
U.S. government and agency securities
Debt Securities, Available-for-sale [Line Items]
Debt securities, fair value	832		892
Debt securities, amortized cost	828		895
Debt securities, unrealized gains	5		2
Debt securities, unrealized losses	(1)		(5)
Foreign government bonds
Debt Securities, Available-for-sale [Line Items]
Debt securities, fair value	99		166
Debt securities, amortized cost	99		167
Debt securities, unrealized gains	0		0
Debt securities, unrealized losses	0		(1)
Mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Debt securities, fair value	8		8
Debt securities, amortized cost	8		8
Debt securities, unrealized gains	0		0
Debt securities, unrealized losses	$ 0		$ 0

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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).

+ References

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Amount, before tax, of unrealized loss 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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Amortized cost of 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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Amount of 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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Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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