Revenue Recognition Summary of Contract Assets and Liabilities (Details) $ in Millions	9 Months Ended
	Sep. 30, 2019 USD ($)
Change in Accounts Receivable [Roll Forward]
Opening balance as of December 31, 2018 (1)	$ 763	[1]
Closing balance as of September 30, 2019	779
Increase (Decrease) in Accounts Receivable	16
Change in Other Accrued Unbilled Revenues [Roll Forward]
Opening balance as of December 31, 2018 (1)	575	[1]
Closing balance as of September 30, 2019	403
Increase (Decrease) in Other Accrued Unbilled Revenues	(172)
Change in Contract Asset [Roll Forward]
Opening balance as of December 31, 2018 (1)	37	[1]
Closing balance as of September 30, 2019	75
Increase (Decrease) in Contract with Customer, Asset	38
Change in Contract Liability [Roll Forward]
Opening balance as of December 31, 2018 (1)	47	[1]
Closing balance as of September 30, 2019	42
Increase (Decrease) in Contract with Customer, Liability	(5)
Contract with Customer, Liability, Revenue Recognized	46
Houston Electric [Member]
Change in Accounts Receivable [Roll Forward]
Opening balance as of December 31, 2018 (1)	234
Closing balance as of September 30, 2019	325
Increase (Decrease) in Accounts Receivable	91
Change in Other Accrued Unbilled Revenues [Roll Forward]
Opening balance as of December 31, 2018 (1)	110
Closing balance as of September 30, 2019	136
Increase (Decrease) in Other Accrued Unbilled Revenues	26
Change in Contract Liability [Roll Forward]
Opening balance as of December 31, 2018 (1)	3
Closing balance as of September 30, 2019	4
Increase (Decrease) in Contract with Customer, Liability	1
Contract with Customer, Liability, Revenue Recognized	3
CERC Corp [Member]
Change in Accounts Receivable [Roll Forward]
Opening balance as of December 31, 2018 (1)	282
Closing balance as of September 30, 2019	137
Increase (Decrease) in Accounts Receivable	(145)
Change in Other Accrued Unbilled Revenues [Roll Forward]
Opening balance as of December 31, 2018 (1)	263
Closing balance as of September 30, 2019	82
Increase (Decrease) in Other Accrued Unbilled Revenues	$ (181)

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