Investments (Amortized Cost, Gross Unrealized Gains And Losses And Fair Value Of Investment Securities Available-For-Sale) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 1,364	$ 1,772
Unrealized Gains	3	1
Unrealized Losses	(6)	(13)
Available-for-sale securities, current	1,361	1,760
U.S. Treasury And Agency Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	576	630
Unrealized Gains	1	1
Unrealized Losses	(4)	(6)
Available-for-sale securities, current	573	625
Corporate And Other Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	371	420
Unrealized Gains	1	0
Unrealized Losses	(1)	(4)
Available-for-sale securities, current	371	416
Certificates of Deposit and Commercial Paper [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	19	296
Unrealized Gains	0	0
Unrealized Losses	0	0
Available-for-sale securities, current	19	296
Asset-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	341	336
Unrealized Gains	1	0
Unrealized Losses	(1)	(2)
Available-for-sale securities, current	341	334
Municipal Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	57	90
Unrealized Gains	0	0
Unrealized Losses	0	(1)
Available-for-sale securities, current	$ 57	$ 89

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

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Amount of investment in debt and equity securities categorized neither as trading securities nor held-to-maturity securities and intended be sold or mature one year or operating cycle, if longer.

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