Debt Key Components of Long-term Debt (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Fair Value Inputs, Discount Rate	1.00%us-gaap_FairValueInputsDiscountRate
Long-term debt	$ 5,495us-gaap_LongTermDebt	$ 5,494us-gaap_LongTermDebt
Long-term Debt
Debt Instrument [Line Items]
Debt Instrument, Unamortized Discount	5
Debt Instrument, Interest Rate During Period	2.54%
Long-term Notes $2.5B
Debt Instrument [Line Items]
Fair Value Inputs, Discount Rate	99.943%
Long-term debt	2,499
Long-term Notes $2.0B
Debt Instrument [Line Items]
Fair Value Inputs, Discount Rate	99.76%
Long-term debt	1,996
Long-term Notes $1.0B
Debt Instrument [Line Items]
Fair Value Inputs, Discount Rate	99.925%
Long-term debt	$ 1,000

The average effective interest rate during the reporting period.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399

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Reference 3: http://www.xbrl.org/2003/role/presentationRef

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- Definition

The amount of debt discount that was originally recognized at the issuance of the instrument that has yet to be amortized.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

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-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28541-108399

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- Definition

Interest rate used to find the present value of an amount to be paid or received in the future as an input to measure fair value. For example, but not limited to, weighted average cost of capital (WACC), cost of capital, cost of equity and cost of debt.

+ References

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

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- Definition

Carrying amount of long-term debt, net of unamortized discount or premium, including current and noncurrent amounts. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

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Reference 2: http://www.xbrl.org/2003/role/presentationRef

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