Marketable Securities (Narrative) (Details) $ in Millions	Dec. 31, 2015 USD ($) security	Dec. 31, 2014 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	$ 6	$ 12
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	6	$ 12
Unrealized losses that arose within the last 12 months	$ 1
Number of available-for-sale securities in unrealized loss position for less than one year \| security	1
Market value of securities that have been in an unrealized loss position for less than 12 months	$ 4
Market value of securities that have been in an unrealized loss position for twelve months or longer	$ 2
Number of available-for-sale securities in unrealized loss position for greater than or equal to one year \| security	1

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27161-111563

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Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for less than twelve months.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27290-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27337-111563

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27337-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
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-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27290-111563

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27290-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27337-111563

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Number of investment positions in available-for-sale investments in a continuous unrealized loss position for less than one year or normal operating cycle, if longer, for which an other-than-temporary impairment (OTTI) has not been recognized in the income statement.

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No definition available.

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