Short-Term And Long-Term Investments And Restricted Deposits (Short-Term And Long-Term Investments And Restricted Deposits By Investment Type) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Schedule Of Investments And Restricted Deposits By Type [Line Items]
Amortized Cost	$ 1,556	$ 946
Available For Sale Securities Gross Unrealized Gain Accumulated In Investments	5	3
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	(4)	(8)
Fair Value	1,557us-gaap_AvailableForSaleSecurities	941us-gaap_AvailableForSaleSecurities
U.S. Treasury Securities And Obligations Of U.S. Government Corporations And Agencies [Member]
Schedule Of Investments And Restricted Deposits By Type [Line Items]
Amortized Cost	393	246
Available For Sale Securities Gross Unrealized Gain Accumulated In Investments	1	0
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	(2)	(7)
Fair Value	392	239
Corporate Securities [Member]
Schedule Of Investments And Restricted Deposits By Type [Line Items]
Amortized Cost	556	294
Available For Sale Securities Gross Unrealized Gain Accumulated In Investments	2	3
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	(2)	(1)
Fair Value	556	296
Restricted Certificates Of Deposit [Member]
Schedule Of Investments And Restricted Deposits By Type [Line Items]
Amortized Cost	6	6
Available For Sale Securities Gross Unrealized Gain Accumulated In Investments	0	0
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	0	0
Fair Value	6	6
Restricted Cash Equivalents [Member]
Schedule Of Investments And Restricted Deposits By Type [Line Items]
Amortized Cost	79	27
Available For Sale Securities Gross Unrealized Gain Accumulated In Investments	0	0
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	0	0
Fair Value	79	27
Municipal Securities, General Obligation [Member]
Schedule Of Investments And Restricted Deposits By Type [Line Items]
Amortized Cost	54	54
Available For Sale Securities Gross Unrealized Gain Accumulated In Investments	0	0
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	0	0
Fair Value	54	54
Municipal Securities, Pre Refunded [Member]
Schedule Of Investments And Restricted Deposits By Type [Line Items]
Amortized Cost	5	11
Available For Sale Securities Gross Unrealized Gain Accumulated In Investments	0	0
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	0	0
Fair Value	5	11
Municipal Securities, Revenue [Member]
Schedule Of Investments And Restricted Deposits By Type [Line Items]
Amortized Cost	101	69
Available For Sale Securities Gross Unrealized Gain Accumulated In Investments	1	0
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	0	0
Fair Value	102	69
Municipal Securities, Variable Rate Demand Notes [Member]
Schedule Of Investments And Restricted Deposits By Type [Line Items]
Amortized Cost	14	29
Available For Sale Securities Gross Unrealized Gain Accumulated In Investments	0	0
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	0	0
Fair Value	14	29
Asset Backed Securities [Member]
Schedule Of Investments And Restricted Deposits By Type [Line Items]
Amortized Cost	180	139
Available For Sale Securities Gross Unrealized Gain Accumulated In Investments	0	0
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	0	0
Fair Value	180	139
Mortgage backed securities
Schedule Of Investments And Restricted Deposits By Type [Line Items]
Amortized Cost	84	34
Available For Sale Securities Gross Unrealized Gain Accumulated In Investments	1	0
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	0	0
Fair Value	85	34
Cost And Equity Method Investments [Member]
Schedule Of Investments And Restricted Deposits By Type [Line Items]
Amortized Cost	68	22
Available For Sale Securities Gross Unrealized Gain Accumulated In Investments	0	0
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	0	0
Fair Value	68	22
Life Insurance Contracts [Member]
Schedule Of Investments And Restricted Deposits By Type [Line Items]
Amortized Cost	16	15
Available For Sale Securities Gross Unrealized Gain Accumulated In Investments	0	0
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	0	0
Fair Value	$ 16	$ 15

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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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

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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- Definition

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

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