Fair Value Measurements (Unrealized Losses And Fair Value Of Investments With Unrealized Losses) (Details) $ in Millions	Mar. 31, 2019 USD ($) investment
Number of Investments \| investment	49
Fair Value \| $	$ 34
Corporate and asset-backed debt securities
Number of Investments \| investment	29
Fair Value \| $	$ 13
United States agency debt securities
Number of Investments \| investment	6
Fair Value \| $	$ 8
United States Treasury debt securities
Number of Investments \| investment	13
Fair Value \| $	$ 12
Certificates of deposit
Number of Investments \| investment	1
Fair Value \| $	$ 1

Number of investment positions in available-for-sale investments in a continuous unrealized loss position for which an other-than-temporary impairment (OTTI) has not been recognized in the income statement.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant