Dispositions (Narrative) (Details) (Salem Harbor, USD $) In Millions, unless otherwise specified	3 Months Ended
Jun. 30, 2012
Salem Harbor
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
(Loss) from discontinued operations, before tax	$ (27)
(Loss) on discontinued operations, net of tax	$ (16)

Pretax provision recognizing a loss for initial, or subsequent, write-down to fair value (less cost to sell) of a disposal group that is classified as a component of the entity, which remains unsold as of the reporting date. May include the recognition of a pretax (gain) for a subsequent increase in fair value (less cost to sell), but not in excess of the cumulative loss previously recognized through write-downs.

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Provision recognizing a loss (after tax benefit) for initial, or subsequent, write-down to fair value (less cost to sell) of a disposal group that is classified as a component of the entity, which remains unsold as of the reporting date. May include the recognition of a (gain) (net of tax expense) for a subsequent increase in fair value (less cost to sell), but not in excess of the cumulative loss previously recognized through write-downs.

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