Fair Value Measurements Fair Value Measurements (Narrative) (Details) (Gas, Transmission and Distribution Equipment, USD $) In Millions, unless otherwise specified	1 Months Ended
Jun. 30, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment charge for certain natural gas infrastructure facilities	$ 49
Impairment charge for certain natural gas infrastructure facilities, net of tax	29
Fair Value, Measurements, Nonrecurring \| Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value (less than $1 million)	$ 1

The aggregate amount of write-downs for impairments recognized during the period for long lived assets held for use (including those held for disposal by means other than sale).

Reference 1: http://www.xbrl.org/2003/role/presentationRef

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Reference 5: http://www.xbrl.org/2003/role/presentationRef

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+ Details