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Income Taxes - Valuation Allowances Rollforward (Detail) (USD $) In Millions, unless otherwise specified					12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2012 Additions [Member]	Dec. 31, 2011 Additions [Member]	Dec. 31, 2010 Additions [Member]	Dec. 31, 2012 Reductions [Member]	Dec. 31, 2011 Reductions [Member]	Dec. 31, 2010 Reductions [Member]
Valuation Allowance [Abstract]
Balance at January 1	$ (922)	$ (555)	$ (454)	$ (418)
Valuation Allowance [Line Items]
Change in valuation allowances					(426)	(138)	(49)	59	37	13
Balance at December 31	$ (922)	$ (555)	$ (454)	$ (418)

Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized.

The amount of the change in the period in the valuation allowance for a specified deferred tax asset.