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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
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Dec. 31, 2013
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Dec. 31, 2012
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| 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 |