Fair Value Measurements (Fair Value Measurements Using Significant Unobservable Inputs) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Commodity Contracts [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 39	$ 36	$ 29	$ 21
Total net gains (losses) included in changes in net assets (realized/unrealized)	5	0	6	8
Transfers out of Level 3	(8)	0	(8)	0
Purchases			21	14
Sales	0	(1)	0	(1)
Settlements	(7)	(5)	(19)	(12)
Ending balance	29	30	29	30
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	5	(1)	6	8
Commodity Contracts [Member] | IPL [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	30	32	26	18
Total net gains (losses) included in changes in net assets (realized/unrealized)	2	(1)	0	7
Transfers out of Level 3	(8)	0	(8)	0
Purchases			16	11
Sales	0	(1)	0	(1)
Settlements	(5)	(4)	(15)	(9)
Ending balance	19	26	19	26
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	2	(1)	0	7
Deferred Proceeds [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	154	194	188	188
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	10	7	(24)	13
Ending balance	164	201	164	201
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	154	194	188	188
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	10	7	(24)	13
Ending balance	164	201	164	201
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