Revenue Recognition Summary of Contract Assets and Liabilities (Details) $ in Millions	6 Months Ended
	Jun. 30, 2019 USD ($)
Change in Accounts Receivable [Roll Forward]
Opening balance as of December 31, 2018 (1)	$ 763	[1]
Closing balance as of June 30, 2019	831
Increase (Decrease) in Accounts Receivable	68
Change in Other Accrued Unbilled Revenues [Roll Forward]
Opening balance as of December 31, 2018 (1)	575	[1]
Closing balance as of June 30, 2019	362
Increase (Decrease) in Other Accrued Unbilled Revenues	(213)
Change in Contract Asset [Roll Forward]
Opening balance as of December 31, 2018 (1)	37	[1]
Closing balance as of June 30, 2019	56
Increase (Decrease) in Contract with Customer, Asset	19
Change in Contract Liability [Roll Forward]
Opening balance as of December 31, 2018 (1)	47	[1]
Closing balance as of June 30, 2019	54
Increase (Decrease) in Contract with Customer, Liability	7
Contract with Customer, Liability, Revenue Recognized	38
Houston Electric [Member]
Change in Accounts Receivable [Roll Forward]
Opening balance as of December 31, 2018 (1)	234
Closing balance as of June 30, 2019	305
Increase (Decrease) in Accounts Receivable	71
Change in Other Accrued Unbilled Revenues [Roll Forward]
Opening balance as of December 31, 2018 (1)	110
Closing balance as of June 30, 2019	122
Increase (Decrease) in Other Accrued Unbilled Revenues	12
Change in Contract Liability [Roll Forward]
Opening balance as of December 31, 2018 (1)	3
Closing balance as of June 30, 2019	5
Increase (Decrease) in Contract with Customer, Liability	2
Contract with Customer, Liability, Revenue Recognized	2
CERC Corp [Member]
Change in Accounts Receivable [Roll Forward]
Opening balance as of December 31, 2018 (1)	282
Closing balance as of June 30, 2019	191
Increase (Decrease) in Accounts Receivable	(91)
Change in Other Accrued Unbilled Revenues [Roll Forward]
Opening balance as of December 31, 2018 (1)	263
Closing balance as of June 30, 2019	87
Increase (Decrease) in Other Accrued Unbilled Revenues	$ (176)

[1] Opening balances related to Vectren are as of February 1, 2019.