Common Stock (Schedule of Intrinsic Value of Options Exercised) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Equity and Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Intrinsic value of options outstanding as of December 31	$ 53	$ 53
Intrinsic value of options outstanding and exercisable (as of December 31)	48	45
Intrinsic value of options exercised	$ 17	$ 21	$ 33
Weighted-average grant date fair value per option	$ 0.00	$ 24.56	$ 29.52

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Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercised in Period, Weighted Average Grant Date Fair Value

+ References

No definition available.

+ Details

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- Definition

Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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- Definition

Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (d)(2)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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- Definition

Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

+ References

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