Income Taxes - Reconciliation of Change in Unrecognized Income Tax Benefits, Excluding Interest and Penalties (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Balance at January 1	$ 169us-gaap_UnrecognizedTaxBenefits	$ 138us-gaap_UnrecognizedTaxBenefits	$ 150us-gaap_UnrecognizedTaxBenefits
Additions for tax positions related to the current year	20	18	8
Additions for tax positions related to prior years	13	41	9
Reductions for tax positions related to prior years	(15)	(8)	(13)
Reductions for tax positions related to settlements with taxing authorities	(1)		(1)
Reduction for tax positions related to prior years as a result of a lapse of statute of limitations	(6)	(20)	(15)
Balance at December 31	$ 180us-gaap_UnrecognizedTaxBenefits	$ 169us-gaap_UnrecognizedTaxBenefits	$ 138us-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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-Publisher FASB

-Name Accounting Standards Codification

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

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

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

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-Publisher FASB

-Name Accounting Standards Codification

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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.

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

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-Name Accounting Standards Codification

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