Fair Value Measurements (Fair Value Measurements Using Significant Unobservable Inputs) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Commodity Contracts [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 36	$ 13	$ 21	$ 12
Total net gains (losses) included in changes in net assets (realized/unrealized)	0	13	8	7
Transfers out of Level 3	0	(1)	0	3
Purchases			14	14
Sales	(1)	0	(1)	0
Settlements	(5)	(3)	(12)	(14)
Ending balance	30	22	30	22
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30	(1)	13	8	10
Commodity Contracts [Member] | IPL [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	32	9	18	9
Total net gains (losses) included in changes in net assets (realized/unrealized)	(1)	12	7	9
Transfers out of Level 3	0	(1)	0	2
Purchases			11	9
Sales	(1)	0	(1)	0
Settlements	(4)	(2)	(9)	(11)
Ending balance	26	18	26	18
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30	(1)	12	7	10
Deferred Proceeds [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	194	215	188	119
Total net gains (losses) included in changes in net assets (realized/unrealized)	0	0	0	0
Transfers out of Level 3	0	0	0	0
Purchases			0	0
Sales	0	0	0	0
Settlements	7	22	13	118
Ending balance	201	237	201	237
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30	0	0	0	0
Deferred Proceeds [Member] | IPL [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	194	215	188	119
Total net gains (losses) included in changes in net assets (realized/unrealized)	0	0	0	0
Transfers out of Level 3	0	0	0	0
Purchases			0	0
Sales	0	0	0	0
Settlements	7	22	13	118
Ending balance	201	237	201	237
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30	$ 0	$ 0	$ 0	$ 0