Reconciliation of Beginning and Ending Amount of Unrecognized Tax Benefits (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Balance at beginning of year	$ 11	$ 10
Additions for tax positions related to the current year	1	4
Additions for tax positions related to prior years	2	3
Reductions for tax positions related to prior years		(2)
Reductions due to lapse of statute of limitations	(1)	(3)
Reductions for settlements with tax authorities		(1)
Balance at end of year	$ 13	$ 11

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The gross amount of unrecognized tax benefits pertaining to uncertain tax positions taken in tax returns as of the balance sheet date.

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The gross amount of decreases in unrecognized tax benefits resulting from tax positions taken in prior period tax returns, excluding amounts pertaining to examined tax returns.

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The gross amount of decreases in unrecognized tax benefits resulting from settlements with taxing authorities.

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The gross amount of increases in unrecognized tax benefits resulting from tax positions that have been or will be taken in the tax return for the current period, excluding amounts pertaining to examined tax returns.

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The gross amount of decreases in unrecognized tax benefits resulting from lapses of the applicable statutes of limitations.

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