Net Income Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
Mar. 31, 2016	Mar. 31, 2015
NUMERATOR:
Net income	$ 511	$ 453
Incremental income effect of interest on 5.25% convertible notes	1	1
Net income after assumed conversion	$ 512	$ 454
DENOMINATOR:
Weighted-average shares outstanding, basic	641	674
Dilutive effect of Employee stock options and restricted stock units	1	2
Dilutive effect of 5.25% convertible notes	6	6
Adjusted weighted-average shares outstanding, diluted	648	682
NET INCOME PER SHARE:
Basic	$ 0.80	$ 0.67
Diluted	$ 0.79	$ 0.66

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of share based payment arrangements using the treasury stock method.

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The after-tax amount of interest recognized in the period associated with any convertible debt.

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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.

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