Summary of Net Deferred Tax Assets (Liabilities) (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Assets
Current deferred income taxes (Other current assets)		$ 21	$ 10
Long-term deferred income taxes	383	348	4
Liabilities
Current deferred income taxes (Other current liabilities)		0	0
Long-term deferred income taxes	(19)	(18)	(72)
Net deferred tax asset (liability)		$ 351	$ (58)

Amount after allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards expected to be realized or consumed within one year or operating cycle, if longer.

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Amount after allocation of valuation allowances of noncurrent deferred tax asset attributable to deductible temporary differences and carryforwards. Noncurrent assets are expected to be realized or consumed after one year (or the normal operating cycle, if longer).

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- Definition

Amount of deferred tax liability attributable to taxable temporary differences, net of deferred tax asset attributable to deductible temporary differences and carryforwards net of valuation allowances expected to be realized or consumed within one year or operating cycle, if longer.

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- Definition

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