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Financial Instruments - Information on Debt and Equity Securities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Debt securities, fair value	$ 7,261	$ 14,908
Publicly traded equity securities, fair value	456
Publicly traded equity securities, fair value		275
Total debt and publicly traded equity securities, fair value	7,717
Total debt and publicly traded equity securities, fair value		15,183
Debt securities, amortized cost	7,340	14,976
Publicly traded equity securities, amortized cost		265
Total debt and publicly traded equity securities, amortized cost		15,241
Debt securities, gross unrealized gains	6	11
Publicly traded equity securities, gross unrealized gains		16
Total debt and publicly traded equity securities, gross unrealized gains		27
Debt securities, gross unrealized losses	(85)	(79)
Publicly traded equity securities, gross unrealized losses		(6)
Total debt and publicly traded equity securities, gross unrealized losses		(85)
Unrealized net gains	35
Commercial paper
Debt Securities, Available-for-sale [Line Items]
Debt securities, fair value	0	159
Debt securities, amortized cost	0	159
Debt securities, gross unrealized gains	0	0
Debt securities, gross unrealized losses	0	0
Corporate notes and bonds
Debt Securities, Available-for-sale [Line Items]
Debt securities, fair value	4,920	9,806
Debt securities, amortized cost	4,985	9,837
Debt securities, gross unrealized gains	3	9
Debt securities, gross unrealized losses	(68)	(40)
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Debt securities, fair value	1,275	1,542
Debt securities, amortized cost	1,285	1,548
Debt securities, gross unrealized gains	1	1
Debt securities, gross unrealized losses	(11)	(7)
U.S. government and agency securities
Debt Securities, Available-for-sale [Line Items]
Debt securities, fair value	892	2,042
Debt securities, amortized cost	895	2,059
Debt securities, gross unrealized gains	2	0
Debt securities, gross unrealized losses	(5)	(17)
Foreign government bonds
Debt Securities, Available-for-sale [Line Items]
Debt securities, fair value	166	733
Debt securities, amortized cost	167	739
Debt securities, gross unrealized gains	0	0
Debt securities, gross unrealized losses	(1)	(6)
Mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Debt securities, fair value	8	626
Debt securities, amortized cost	8	634
Debt securities, gross unrealized gains	0	1
Debt securities, gross unrealized losses	$ 0	$ (9)

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