Commitments And Contingencies (MPG Site Estimated Future Costs And Recorded Liabilities) (Details) - Manufactured Gas Plant Sites [Member] $ in Millions	9 Months Ended
	Sep. 30, 2017 USD ($)
Commitments and Contingencies [Line Items]
Minimum range of estimated future costs	$ 12
Maximum range of estimated future costs	31
Current and non-current environmental liabilities	16
IPL [Member]
Commitments and Contingencies [Line Items]
Minimum range of estimated future costs	10
Maximum range of estimated future costs	27
Current and non-current environmental liabilities	$ 14