Revenue (Disaggregation of Revenues) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 1,024	$ 920	$ 2,742	$ 2,599
Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	939	852	2,357	2,257
Electric [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	348	328	868	845
Electric [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	232	210	579	556
Electric [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	265	241	677	648
Electric [Member] | Wholesale [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	55	47	142	127
Electric [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	39	26	91	81
Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	50	42	289	253
Gas [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	24	22	162	146
Gas [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	13	10	85	70
Gas [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	3	2	11	8
Gas [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	10	8	31	29
Other Utility [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	13	10	36	32
Other Utility [Member] | Steam [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	9	8	27	27
Other Utility [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	4	2	9	5
Non-utility and Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	22	16	60	57
Non-utility and Other [Member] | Travero and other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	22	16	60	57
IPL [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	599	553	1,543	1,504
IPL [Member] | Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	555	519	1,343	1,332
IPL [Member] | Electric [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	207	189	488	472
IPL [Member] | Electric [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	160	142	385	371
IPL [Member] | Electric [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	158	149	386	384
IPL [Member] | Electric [Member] | Wholesale [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	18	17	44	44
IPL [Member] | Electric [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	12	22	40	61
IPL [Member] | Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	31	24	165	141
IPL [Member] | Gas [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	14	12	90	79
IPL [Member] | Gas [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	8	6	47	38
IPL [Member] | Gas [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	3	1	8	5
IPL [Member] | Gas [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	6	5	20	19
IPL [Member] | Other Utility [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	13	10	35	31
IPL [Member] | Other Utility [Member] | Steam [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	9	8	27	27
IPL [Member] | Other Utility [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	4	2	8	4
WPL [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	403	351	1,139	1,038
WPL [Member] | Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	384	333	1,014	925
WPL [Member] | Electric [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	141	139	380	373
WPL [Member] | Electric [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	72	68	194	185
WPL [Member] | Electric [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	107	92	291	264
WPL [Member] | Electric [Member] | Wholesale [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	37	30	98	83
WPL [Member] | Electric [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	27	4	51	20
WPL [Member] | Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	19	18	124	112
WPL [Member] | Gas [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	10	10	72	67
WPL [Member] | Gas [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	5	4	38	32
WPL [Member] | Gas [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	1	3	3
WPL [Member] | Gas [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	4	3	11	10
WPL [Member] | Other Utility [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	1	1
WPL [Member] | Other Utility [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 0	$ 0	$ 1	$ 1