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Financial Instruments - Information on Available-for-sale Investments (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Debt securities, fair value	$ 12,587	$ 12,587	$ 14,908
Publicly traded equity securities, fair value	375	375
Publicly traded equity securities, fair value			275
Total debt and publicly traded equity securities, fair value	12,962	12,962
Total debt and publicly traded equity securities, fair value			15,183
Debt securities, amortized cost	12,752	12,752	14,976
Publicly traded equity securities, amortized cost			265
Total debt and publicly traded equity securities, amortized cost			15,241
Debt securities, unrealized gains	3	3	11
Equity securities, unrealized gains			16
Total debt and publicly traded equity securities, unrealized gains			27
Debt securities, unrealized losses	(168)	(168)	(79)
Equity securities, unrealized losses			(6)
Total debt and publicly traded equity securities, unrealized losses			(85)
Unrealized net gain	7	50
Commercial paper
Debt Securities, Available-for-sale [Line Items]
Debt securities, fair value	30	30	159
Debt securities, amortized cost	30	30	159
Debt securities, unrealized gains	0	0	0
Debt securities, unrealized losses	0	0	0
Corporate notes and bonds
Debt Securities, Available-for-sale [Line Items]
Debt securities, fair value	8,782	8,782	9,806
Debt securities, amortized cost	8,902	8,902	9,837
Debt securities, unrealized gains	2	2	9
Debt securities, unrealized losses	(122)	(122)	(40)
U.S. government and agency securities
Debt Securities, Available-for-sale [Line Items]
Debt securities, fair value	1,620	1,620	2,042
Debt securities, amortized cost	1,640	1,640	2,059
Debt securities, unrealized gains	0	0	0
Debt securities, unrealized losses	(20)	(20)	(17)
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Debt securities, fair value	1,441	1,441	1,542
Debt securities, amortized cost	1,456	1,456	1,548
Debt securities, unrealized gains	1	1	1
Debt securities, unrealized losses	(16)	(16)	(7)
Foreign government bonds
Debt Securities, Available-for-sale [Line Items]
Debt securities, fair value	649	649	733
Debt securities, amortized cost	658	658	739
Debt securities, unrealized gains	0	0	0
Debt securities, unrealized losses	(9)	(9)	(6)
Mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Debt securities, fair value	65	65	626
Debt securities, amortized cost	66	66	634
Debt securities, unrealized gains	0	0	1
Debt securities, unrealized losses	$ (1)	$ (1)	$ (9)

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Debt Securities and Equity Securities, FV-NI

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