Income Taxes (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Income Taxes
Effective tax rate (as a percent)	18.00%	10.00%
Maximum period for recognizing capital losses	5 years
Valuation Allowance	$ 5		$ 5
Gross unrecognized tax benefits	65		65
Unrecognized tax benefits, net of federal tax benefits that would affect the effective tax rate if recognized	8		8
Estimated decrease in amount of unrecognized tax benefits in next 12 months	63
Net increase (decrease) in interest and penalties	2	(5)
Payable (receivable) related to accrued interest and penalties	$ 32		$ 30

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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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

This element represents the total of accruals as of the date of the statement of financial position for interest 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 and the amount of statutory penalties for a tax position claimed or expected to be claimed by the entity, in its tax return, that does not meet the minimum statutory threshold to avoid payment of penalties.

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- Definition

This element represents the total of 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 and 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.

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