Commitments and Contingencies (Cost and Equity Investees and Other Entities) (Narrative) (Details) - Joint Venture [Member]	Dec. 31, 2016	Sep. 30, 2016
Joint Ventures That Provide Electrical Transmission Infrastructure Services [Member]
Other Commitments [Line Items]
Number of joint ventures	3
Joint Venture A That Provides Electrical Transmission Infrastructure Services [Member]
Other Commitments [Line Items]
Proportionately consolidated non-controlled joint venture, ownership percentage	85.00%
Joint Venture B That Provides Electrical Transmission Infrastructure Services [Member]
Other Commitments [Line Items]
Proportionately consolidated non-controlled joint venture, ownership percentage	85.00%
Joint Venture C That Provides Electrical Transmission Infrastructure Services [Member]
Other Commitments [Line Items]
Proportionately consolidated non-controlled joint venture, ownership percentage	90.00%
Pacer [Member]
Other Commitments [Line Items]
Proportionately consolidated non-controlled joint venture, ownership percentage	35.00%	35.00%