Income Taxes - Unrecognized Tax Benefits (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Unrecognized Tax Benefits [Roll Forward]
Beginning Balance	$ 142us-gaap_UnrecognizedTaxBenefits	$ 333us-gaap_UnrecognizedTaxBenefits	$ 532us-gaap_UnrecognizedTaxBenefits
Additions based on tax positions related to the current year	20	1	10
Additions for tax positions of prior years	0	7	3
Reductions for tax positions for prior years	(2)	(50)	(204)
Settlements	0	(82)	(8)
Expiration of statutes	(80)	(67)	0
Ending Balance	$ 80us-gaap_UnrecognizedTaxBenefits	$ 142us-gaap_UnrecognizedTaxBenefits	$ 333us-gaap_UnrecognizedTaxBenefits

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Amount of unrecognized tax benefits pertaining to uncertain tax positions taken in tax returns.

+ References

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-Publisher FASB

-Name Accounting Standards Codification

-Glossary Unrecognized Tax Benefit

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Amount of decrease in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.

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-Publisher FASB

-Name Accounting Standards Codification

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Amount of decrease in unrecognized tax benefits resulting from settlements with taxing authorities.

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Amount of increase in unrecognized tax benefits resulting from tax positions that have been or will be taken in current period tax return.

+ References

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Amount of increase in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.

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Amount of decrease in unrecognized tax benefits resulting from lapses of applicable statutes of limitations.

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