Commitments And Contingencies (Other Purchase Obligations) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($)
Long-term Purchase Commitment [Line Items]
Minimum future commitments	$ 2,410
Individual commitments incurred	1
Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	1,232	[1]
Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	946
Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	192	[2]
Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	40	[3]
2018 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	545
2018 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	188	[1]
2018 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	229
2018 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	107	[2]
2018 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	21	[3]
2019 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	364
2019 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	159	[1]
2019 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	140
2019 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	59	[2]
2019 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	6	[3]
2020 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	292
2020 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	135	[1]
2020 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	130
2020 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	21	[2]
2020 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	6	[3]
2021 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	267
2021 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	149	[1]
2021 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	110
2021 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	5	[2]
2021 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	3	[3]
2022 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	226
2022 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	140	[1]
2022 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	84
2022 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[2]
2022 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	2	[3]
Thereafter [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	716
Thereafter [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	461	[1]
Thereafter [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	253
Thereafter [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[2]
Thereafter [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	2	[3]
IPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	1,669
IPL [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	1,159	[1]
IPL [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	384
IPL [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	98	[2]
IPL [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	28	[3]
IPL [Member] | 2018 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	322
IPL [Member] | 2018 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	130	[1]
IPL [Member] | 2018 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	126
IPL [Member] | 2018 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	51	[2]
IPL [Member] | 2018 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	15	[3]
IPL [Member] | 2019 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	236
IPL [Member] | 2019 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	144	[1]
IPL [Member] | 2019 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	58
IPL [Member] | 2019 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	31	[2]
IPL [Member] | 2019 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	3	[3]
IPL [Member] | 2020 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	193
IPL [Member] | 2020 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	135	[1]
IPL [Member] | 2020 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	44
IPL [Member] | 2020 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	11	[2]
IPL [Member] | 2020 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	3	[3]
IPL [Member] | 2021 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	189
IPL [Member] | 2021 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	149	[1]
IPL [Member] | 2021 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	32
IPL [Member] | 2021 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	5	[2]
IPL [Member] | 2021 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	3	[3]
IPL [Member] | 2022 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	164
IPL [Member] | 2022 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	140	[1]
IPL [Member] | 2022 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	22
IPL [Member] | 2022 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[2]
IPL [Member] | 2022 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	2	[3]
IPL [Member] | Thereafter [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	565
IPL [Member] | Thereafter [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	461	[1]
IPL [Member] | Thereafter [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	102
IPL [Member] | Thereafter [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[2]
IPL [Member] | Thereafter [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	2	[3]
WPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	735
WPL [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	73	[1]
WPL [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	562
WPL [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	94	[2]
WPL [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	6	[3]
WPL [Member] | 2018 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	222
WPL [Member] | 2018 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	58	[1]
WPL [Member] | 2018 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	103
WPL [Member] | 2018 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	56	[2]
WPL [Member] | 2018 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	5	[3]
WPL [Member] | 2019 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	126
WPL [Member] | 2019 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	15	[1]
WPL [Member] | 2019 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	82
WPL [Member] | 2019 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	28	[2]
WPL [Member] | 2019 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	1	[3]
WPL [Member] | 2020 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	96
WPL [Member] | 2020 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[1]
WPL [Member] | 2020 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	86
WPL [Member] | 2020 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	10	[2]
WPL [Member] | 2020 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[3]
WPL [Member] | 2021 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	78
WPL [Member] | 2021 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[1]
WPL [Member] | 2021 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	78
WPL [Member] | 2021 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[2]
WPL [Member] | 2021 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[3]
WPL [Member] | 2022 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	62
WPL [Member] | 2022 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[1]
WPL [Member] | 2022 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	62
WPL [Member] | 2022 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[2]
WPL [Member] | 2022 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[3]
WPL [Member] | Thereafter [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	151
WPL [Member] | Thereafter [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[1]
WPL [Member] | Thereafter [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	151
WPL [Member] | Thereafter [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[2]
WPL [Member] | Thereafter [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	$ 0	[3]

[1] Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased.

[2] Corporate Services entered into system-wide coal contracts on behalf of IPL and WPL that include minimum future commitments. These commitments were assigned to IPL and WPL based on information available as of December 31, 2017 regarding expected future usage, which is subject to change.

[3] Includes individual commitments incurred during the normal course of business that exceeded $1 million at December 31, 2017.