Income Taxes (Schedule Of Deferred Tax Assets And Liabilities) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Deferred tax liabilities:
Differences between book and tax basis of property	$ 2,504	$ 2,115
Derivative activity	122	13
Other	21us-gaap_DeferredTaxLiabilitiesOther	11us-gaap_DeferredTaxLiabilitiesOther
Total deferred tax liabilities	2,647us-gaap_DeferredTaxLiabilities	2,139us-gaap_DeferredTaxLiabilities
Deferred tax assets
Accrued compensation	23	16
Alternative minimum tax credit carryforward	131	77
Stored natural gas	5us-gaap_DeferredTaxAssetsInventory	9us-gaap_DeferredTaxAssetsInventory
Accrued pension costs	17	2
Asset retirement obligations	79	54
Net operating loss carryforward	318us-gaap_OperatingLossCarryforwards	412us-gaap_OperatingLossCarryforwards
Differences between book and tax basis of property - state	6	11
Other	8us-gaap_DeferredTaxAssetsOther	7us-gaap_DeferredTaxAssetsOther
Total deferred tax assets	587us-gaap_DeferredTaxAssetsNet	588us-gaap_DeferredTaxAssetsNet
Net deferred tax liability	$ 2,060us-gaap_DeferredTaxAssetsLiabilitiesNet	$ 1,551us-gaap_DeferredTaxAssetsLiabilitiesNet

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from asset retirement obligations. An asset retirement obligation is a legal obligation associated with the disposal or retirement from service of a tangible long-lived asset.

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