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Income Taxes - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2013 BusinessTaxProvision	Mar. 31, 2012	Dec. 31, 2012
Income Taxes [Line Items]
Effective tax rate	27.40%	28.30%
U.S. federal statutory rate	35.00%	35.00%
Income tax benefit	$ 64	$ 39
Number of specific temporary business tax provisions expired during the period	2
Tax provision due to two specific temporary business tax provision that expired in 2011			19
American Taxpayer Relief Act of 2012 [Member]
Income Taxes [Line Items]
Income tax benefit	$ 19

A ratio calculated by dividing the reported amount of income tax expense attributable to continuing operations for the period by GAAP-basis pretax income from continuing operations.

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- Definition

The domestic federal statutory tax rate applicable under enacted tax laws to the Company's pretax income from continuing operations for the period. The "statutory" tax rate is the regular tax rate if there are alternative tax systems.

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- Definition

The sum of the current income tax expense or benefit and the deferred income tax expense or benefit pertaining to continuing operations.

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