Stock-Based Compensation (Details) (USD $) In Millions, except Per Share data	12 Months Ended
Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Summary of stock option activity and related information
Options Outstanding, Beginning Balance	13.0
Weighted Average Exercise Price, Beginning Balance	$ 16.73
Options, Granted	1.3
Weighted Average Exercise Price, Granted	$ 21.20
Options, Exercised	(1.2)
Weighted Average Exercise Price, Exercised	$ 6.11
Aggregate Intrinsic Value, Exercised	$ 20	$ 2	$ 49
Options, Expired	(0.3)
Weighted Average Exercise Price, Expired	$ 40.89
Options, Forfeited	(0.1)
Weighted Average Exercise Price, Forfeited	$ 17.71
Options Outstanding, Ending Balance	12.7	13.0
Weighted Average Exercise Price, Ending Balance	$ 17.59	$ 16.73
Aggregate Intrinsic Value, Ending Balance	109
Options Exercisable at December 31, 2010	9.8
Weighted Average Exercise Price, Exercisable at December 31, 2010	$ 17.44
Aggregate Intrinsic Value, Exercisable at December 31, 2010	$ 86

The total dollar difference between fair values of the underlying shares reserved for issuance and exercise prices of vested portions of options outstanding and currently exercisable under the option plan as of the balance-sheet date.

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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.

+ References

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-Name Statement of Financial Accounting Standard (FAS)
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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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The decrease in the number of reserved shares that could potentially be issued attributable to the exercise or conversion during the reporting period of previously issued stock options under the option plan.

+ References

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The total accumulated difference between fair values of underlying shares on dates of exercise and exercise price on options which were exercised (or share units converted) into shares during the reporting period under the plan.

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- Definition

The weighted average price at which option holders acquired shares when converting their stock options into shares under the plan during the reporting period.

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The decrease in the number of shares that could be issued attributable to the lapse of rights to exercise previously issued stock options under the terms of the option agreements under the plan during the reporting period.

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The weighted average price at which grantees could have acquired the underlying shares with respect to stock options of the plan that lapsed during the reporting period.

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- Definition

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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The weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated during the reporting period due to noncompliance with plan terms during the reporting period.

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The quantity of shares issuable on stock options awarded under the plan during the reporting period.

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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 stock options awarded under the plan during the reporting period.

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- Definition

The total dollar difference between fair values of the underlying shares reserved for issuance and exercise prices pertaining to options outstanding under the plan as of the balance-sheet date.

+ References

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- Definition

The number of shares reserved for issuance under stock option agreements awarded under the plan that validly exist and are outstanding as of the balance-sheet date, including vested options.

+ References

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-Publisher FASB
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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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The weighted average price as of the beginning of the year at which grantees can acquire the shares reserved for issuance under the stock option plan.

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