Common Equity (Changes in Shareowners' Equity) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance			$ 5,688
Beginning balance	$ 6,019	$ 5,748	5,888	$ 5,405
Net income attributable to common shareowners	256	246	571	550
Net income	259	249	579	558
Common stock dividends	(101)	(94)	(304)	(281)
Equity forward settlements and Shareowner Direct Plan issuances	6	6	22	241
Equity-based compensation plans and other	5	3	8	5
Adoption of new accounting standard, net of tax	(3,261)		(3,261)		$ (2,994)
Other comprehensive loss, net of tax				(2)
Ending balance	5,985		5,985
Ending balance	$ 6,185	$ 5,909	$ 6,185	$ 5,909
Common stock dividends (in dollars per share)	$ 0.4025	$ 0.38	$ 1.2075	$ 1.14
Common Stock [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	$ 3	$ 2	$ 2	$ 2
Equity forward settlements and Shareowner Direct Plan issuances			1
Ending balance	3	2	3	2
Additional Paid-in Capital [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	2,722	2,683	2,704	2,446
Equity forward settlements and Shareowner Direct Plan issuances	6	6	21	241
Equity-based compensation plans and other	5	4	8	6
Ending balance	2,733	2,693	2,733	2,693
Retained Earnings [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	3,106	2,874	2,994	2,766
Net income attributable to common shareowners	256	246	571	550
Common stock dividends	(101)	(94)	(304)	(281)
Ending balance	3,261	3,026	3,261	3,026
Accumulated Other Comprehensive Income (Loss) [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	(1)	(1)	(1)	1
Other comprehensive loss, net of tax				(2)
Ending balance	(1)	(1)	(1)	(1)
Shares in Deferred Compensation Trust [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	(11)	(10)	(11)	(10)
Equity-based compensation plans and other		(1)		(1)
Ending balance	(11)	(11)	(11)	(11)
Cumulative Preferred Stock [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	200	200	200	200
Ending balance	200	200	200	200
IPL [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance			3,764
Beginning balance	3,979	3,671	3,964	3,472
Net income attributable to common shareowners	157	148	322	290
Net income	160	151	330	298
Common stock dividends	(101)	(59)	(301)	(177)
Adoption of new accounting standard, net of tax	(1,000)		(1,000)		(979)
Capital contributions from parent		170	50	345
Ending balance	3,835		3,835
Ending balance	4,035	3,930	4,035	3,930
IPL [Member] | Common Stock [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	33	33	33	33
Ending balance	33	33	33	33
IPL [Member] | Additional Paid-in Capital [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	2,802	2,523	2,752	2,348
Capital contributions from parent		170	50	345
Ending balance	2,802	2,693	2,802	2,693
IPL [Member] | Retained Earnings [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	944	915	979	891
Net income attributable to common shareowners	157	148	322	290
Common stock dividends	(101)	(59)	(301)	(177)
Ending balance	1,000	1,004	1,000	1,004
IPL [Member] | Cumulative Preferred Stock [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	200	200	200	200
Ending balance	200	200	200	200
WPL [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance			2,478
Beginning balance	2,725	2,452	2,478	2,364
Net income	93	73	215	220
Common stock dividends	(41)	(43)	(126)	(127)
Adoption of new accounting standard, net of tax	(1,042)		(1,042)		$ (953)
Capital contributions from parent	35		245	25
Ending balance	2,812		2,812
Ending balance	2,812	2,482	2,812	2,482
WPL [Member] | Common Stock [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	66	66	66	66
Ending balance	66	66	66	66
WPL [Member] | Additional Paid-in Capital [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	1,669	1,459	1,459	1,434
Capital contributions from parent	35		245	25
Ending balance	1,704	1,459	1,704	1,459
WPL [Member] | Retained Earnings [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	990	927	953	864
Net income	93	73	215	220
Common stock dividends	(41)	(43)	(126)	(127)
Ending balance	$ 1,042	$ 957	$ 1,042	$ 957
Credit Losses ASU [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Adoption of new accounting standard, net of tax						$ (9)
Credit Losses ASU [Member] | Retained Earnings [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Adoption of new accounting standard, net of tax						$ (9)