Income Taxes - Unrecognized Tax Benefits (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Reconciliation of tnrecognized tax benefits
Balance at beginning of year	$ 111us-gaap_UnrecognizedTaxBenefits	$ 165us-gaap_UnrecognizedTaxBenefits	$ 153us-gaap_UnrecognizedTaxBenefits
Additions based on tax positions related to the current year	0	0	8
Additions for tax positions of prior years	3	3	49
Reductions for tax positions of prior years	(3)	(41)	(27)
Settlements	(18)	(8)	(18)
Reductions for lapse of statute of limitations	0	(8)	0
Balance at end of year	$ 93us-gaap_UnrecognizedTaxBenefits	$ 111us-gaap_UnrecognizedTaxBenefits	$ 165us-gaap_UnrecognizedTaxBenefits

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Unrecognized Tax Benefit

-URI http://asc.fasb.org/extlink&oid=6527854

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

+ References

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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.

+ References

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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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