Fair Value Measurements (Fair Value Measurements Using Significant Unobservable Inputs) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Commodity Contracts [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 15	$ 14	$ 29	$ 21
Total net gains (losses) included in changes in net assets (realized/unrealized)	8	12	1	9
Purchases	21	14	21	14
Settlements	(5)	(4)	(12)	(8)
Ending balance	39	36	39	36
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 June 30	8	12	1	9
Commodity Contracts [Member] | IPL [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	14	13	26	18
Total net gains (losses) included in changes in net assets (realized/unrealized)	4	11	(2)	9
Purchases	16	11	16	11
Settlements	(4)	(3)	(10)	(6)
Ending balance	30	32	30	32
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 June 30	4	11	(2)	9
Deferred Proceeds [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	107	188	188	188
Total net gains (losses) included in changes in net assets (realized/unrealized)	0	0	0	0
Purchases	0	0	0	0
Settlements	47	6	(34)	6
Ending balance	154	194	154	194
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 June 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	107	188	188	188
Total net gains (losses) included in changes in net assets (realized/unrealized)	0	0	0	0
Purchases	0	0	0	0
Settlements	47	6	(34)	6
Ending balance	154	194	154	194
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 June 30	$ 0	$ 0	$ 0	$ 0