Debt (Details) - Senior notes - USD ($) $ in Millions	Jun. 30, 2015	May. 26, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Long-term debt	$ 1,494		$ 799
5.9% Senior Notes, due 2017
Debt Instrument [Line Items]
Long-term debt	$ 400		$ 400
Interest rate	5.90%		5.90%
Unamortized debt discount on senior notes (less than $1 million for 5.9% Senior Notes)	$ 1
4.0% Senior Notes, due 2025
Debt Instrument [Line Items]
Long-term debt	$ 695		$ 0
Interest rate	4.00%	4.00%	4.00%
Unamortized debt discount on senior notes (less than $1 million for 5.9% Senior Notes)	$ 5
6.55% Senior Notes, due 2037
Debt Instrument [Line Items]
Long-term debt	$ 399		$ 399
Interest rate	6.55%		6.55%
Unamortized debt discount on senior notes (less than $1 million for 5.9% Senior Notes)	$ 1

Contractual interest rate for funds borrowed, under the debt agreement.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22(a)(1))

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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

-Section 45

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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 FASB

-Name Accounting Standards Codification

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