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

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This element represents the recognized expense for the amount of statutory penalties in the period in which the entity claims or expects to claim a tax position, in its tax return, that does not meet the minimum statutory threshold to avoid payment of penalties or, if not recognizing the expense in the period in which the tax return was initially filed, the expense is generally recognized in the period in which the enterprise's judgment about meeting the minimum statutory threshold changes.

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- Definition

This element represents interest expense recognized for an underpayment of income taxes computed by applying the applicable statutory rate of interest to the difference between a tax position recognized for financial reporting purposes and the amount previously taken or expected to be taken in a tax return of the entity.

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- Definition

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

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Income Taxes Income taxes (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2011	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012
Operating Loss Carryforwards [Line Items]
Tax Credit Carryforward, Federal				$ 41
Tax Credit Carryforward, State				14
Deferred Tax Assets, Valuation Allowance				0
Valuation Allowance, Deferred Tax Asset, Change in Amount		(2)
Unrecognized Tax Benefits		0	2	0
Unrecognized Tax Benefits, Interest on Income Taxes Expense			1
Unrecognized Tax Benefits, Income Tax Penalties Expense			0
Unrecognized Tax Benefits, Decreases Resulting from Current Period Tax Positions	$ 2