Income Taxes - Reconciliation of Beginning and Ending Amounts of Unrecognized Tax Benefits (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Balance at January 1	$ 570us-gaap_UnrecognizedTaxBenefits	$ 523us-gaap_UnrecognizedTaxBenefits
Additions based on tax positions taken in the current year	42	161
Additions based on tax positions of prior years	70	2
Reductions based on tax positions of prior years	(76)	(96)
Reductions due to settlements with taxing authorities	(3)	(19)
Reductions due to lapses in statutes of limitation		(1)
Balance at December 31	$ 603us-gaap_UnrecognizedTaxBenefits	$ 570us-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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-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.

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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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-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.

+ 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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