Oncor-Related Transactions (Details) - USD ($) $ in Millions	Sep. 30, 2017	Oct. 31, 2016	Jul. 29, 2016
Energy Future Holdings Corp. [Member]
Business Acquisition [Line Items]
Percentage of interests to be acquired in pending merger			100.00%
Energy Future Holdings Corp., Texas Transmission Holdings Corporation, and Oncor Management Investment LLC [Member] | Oncor Electric Delivery Company LLC [Member]
Business Acquisition [Line Items]
Percentage of interests to be acquired in pending merger		100.00%
Energy Future Holdings Corp. [Member]
Business Acquisition [Line Items]
Termination fee sought			$ 275.0
Energy Future Holdings Corp. [Member] | Oncor Electric Delivery Company LLC [Member]
Business Acquisition [Line Items]
Percentage of interests to be acquired in pending merger			80.00%
Texas Transmission Holdings Corporation [Member]
Business Acquisition [Line Items]
Possible termination fee amount transaction not approved	$ 72.3