Revenue Recognition Summary of Contract Assets and Liabilities (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($)
Change in Accounts Receivable [Roll Forward]
Opening balance as of December 31, 2018 (1)	$ 516	[1]
Closing balance as of December 31, 2019	800
Increase (Decrease) in Accounts Receivable	284
Change in Other Accrued Unbilled Revenues [Roll Forward]
Opening balance as of December 31, 2018 (1)	373	[1]
Closing balance as of December 31, 2019	579
Increase (Decrease) in Other Accrued Unbilled Revenues	206
Change in Contract Asset [Roll Forward]
Opening balance as of December 31, 2018 (1)	0	[1]
Closing balance as of December 31, 2019	61
Increase (Decrease) in Contract with Customer, Asset	61
Change in Contract Liability [Roll Forward]
Opening balance as of December 31, 2018 (1)	3	[1]
Closing balance as of December 31, 2019	34
Increase (Decrease) in Contract with Customer, Liability	31
Contract with Customer, Liability, Revenue Recognized	47
Houston Electric [Member]
Change in Accounts Receivable [Roll Forward]
Opening balance as of December 31, 2018 (1)	234
Closing balance as of December 31, 2019	210
Increase (Decrease) in Accounts Receivable	(24)
Change in Other Accrued Unbilled Revenues [Roll Forward]
Opening balance as of December 31, 2018 (1)	110
Closing balance as of December 31, 2019	117
Increase (Decrease) in Other Accrued Unbilled Revenues	7
Change in Contract Liability [Roll Forward]
Opening balance as of December 31, 2018 (1)	3
Closing balance as of December 31, 2019	3
Increase (Decrease) in Contract with Customer, Liability	0
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 December 31, 2019	282
Increase (Decrease) in Accounts Receivable	0
Change in Other Accrued Unbilled Revenues [Roll Forward]
Opening balance as of December 31, 2018 (1)	263
Closing balance as of December 31, 2019	250
Increase (Decrease) in Other Accrued Unbilled Revenues	$ (13)

[1] Opening balances related to Vectren are as of February 1, 2019, and are thus excluded from the opening balance as of December 31, 2018.