Stock-Based Compensation (Details 3) (Stock Options, USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Stock Options
Stock Options
Vesting period	5 years
Expiration period	10 years
Shares
Outstanding at the beginning of the period (in shares)	18,000,000	24,000,000
Granted (in shares)	452,380
Exercised (in shares)	1,000,000	1,000,000
Forfeited (in shares)	136,040
Outstanding at the end of the period (in shares)	17,000,000	23,000,000
Option shares vested and expected to vest at the end of the period	17,000,000	23,000,000
Option shares exercisable at the end of the period	15,000,000	20,000,000
Weighted average exercise price
Outstanding at the beginning of the period (in dollars per share)	$ 21	$ 22
Granted (in dollars per share)	$ 26	$ 22
Exercised (in dollars per share)	$ 14	$ 16
Forfeited (in dollars per share)	$ 22	$ 27
Outstanding at the end of the period (in dollars per share)	$ 22	$ 22
Option shares vested and expected to vest at the end of the period (in dollars per share)	$ 22	$ 22
Option shares exercisable at the end of the period (in dollars per share)	$ 22	$ 23
Aggregate intrinsic value
Exercised	$ 17	$ 10
Option shares vested and expected to vest at the end of the period	108	93
Option shares exercisable at the end of the period	94	72
Weighted average remaining option term
Outstanding at the end of the period	3 years	4 years
Option shares vested and expected to vest at the end of the period	3 years	4 years
Option shares exercisable at the end of the period	3 years	3 years
Additional disclosures
Total unrecognized compensation expense	$ 9	$ 11
Weighted average remaining vesting period	3 years	3 years

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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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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.

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The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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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.

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The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.

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Gross number of share options (or share units) granted during the period.

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Number of options outstanding, including both vested and non-vested options.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Amount by which the current fair value of the underlying stock exceeds the exercise price of fully vested and expected to vest options outstanding.

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As of the balance sheet date, the number of shares into which fully vested and expected to vest stock options outstanding can be converted under the option plan.

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As of the balance sheet date, the weighted-average exercise price for outstanding stock options that are fully vested or expected to vest.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated.

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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Number of share options (or share units) exercised during the current period.

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