Employee Benefit Plans (Details) - Other Postretirement Benefit Plans [Member] - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Defined Benefit Plan Disclosure [Line Items]
Service cost		$ 0	$ 0	$ 0	$ 1
Interest cost		3	2	7	8
Expected return on plan assets		(1)	(1)	(3)	(4)
Amortization of prior service credit		(2)	(1)	(4)	(2)
Curtailment gain (1)	[1]	0	0	0	(3)
Net periodic cost (2)	[2]	0	$ 0	0	$ 0
Expected contribution to postretirement benefit plan in current year				9
Total contribution to the plan during the period		$ 2		$ 7

[1] A curtailment gain or loss is required when the expected future services of a significant number of current employees are reduced or eliminated for the accrual of benefits. In May 2016, Houston Electric entered into a renegotiated collective bargaining agreement with the IBEW Local Union 66 that provides that for Houston Electric union employees covered under the agreement who retire on or after January 1, 2017, retiree medical and prescription drug coverage will be provided exclusively through the NECA/IBEW Family Medical Care Plan in exchange for the payment of monthly premiums as determined under the agreement. As a result, the accrued postretirement benefits related to such future Houston Electric union retirees were eliminated. In 2016, Houston Electric recognized a curtailment gain of $3 million as an accelerated recognition of the prior service credit that would otherwise be recognized in future periods.

[2] Net periodic cost in this table is before considering amounts subject to overhead allocations for capital expenditure projects or for amounts subject to deferral for regulatory purposes.