Commitments And Contingencies (Operating Expense Purchase Obligations) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2007	Dec. 31, 2011
Long-term Purchase Commitment [Line Items]
Minimum future commitments	$ 2,360
Individual commitments incurred	1
Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	1,746	[1]
DAEC IPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	1,538	[1],[2]
Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	208	[1]
Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	278
Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	291	[3]
SO2 emission allowances [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	34	[4]
Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	11	[5]
2015 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	514
2015 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	193	[1]
2015 [Member] | DAEC IPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	119	[1],[2]
2015 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	74	[1]
2015 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	175
2015 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	124	[3]
2015 [Member] | SO2 emission allowances [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	12	[4]
2015 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	10	[5]
2016 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	333
2016 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	171	[1]
2016 [Member] | DAEC IPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	125	[1],[2]
2016 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	46	[1]
2016 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	69
2016 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	78	[3]
2016 [Member] | SO2 emission allowances [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	14	[4]
2016 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	1	[5]
2017 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	260
2017 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	182	[1]
2017 [Member] | DAEC IPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	138	[1],[2]
2017 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	44	[1]
2017 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	23
2017 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	47	[3]
2017 [Member] | SO2 emission allowances [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	8	[4]
2017 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[5]
2018 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	214
2018 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	175	[1]
2018 [Member] | DAEC IPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	131	[1],[2]
2018 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	44	[1]
2018 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	5
2018 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	34	[3]
2018 [Member] | SO2 emission allowances [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[4]
2018 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[5]
2019 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	153
2019 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	143	[1]
2019 [Member] | DAEC IPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	143	[1],[2]
2019 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[1]
2019 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	2
2019 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	8	[3]
2019 [Member] | SO2 emission allowances [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[4]
2019 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[5]
Thereafter [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	886
Thereafter [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	882	[1]
Thereafter [Member] | DAEC IPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	882	[1],[2]
Thereafter [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[1]
Thereafter [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	4
Thereafter [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[3]
Thereafter [Member] | SO2 emission allowances [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[4]
Thereafter [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[5]
IPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	1,859
IPL [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	1,539	[1]
IPL [Member] | DAEC IPL [Member]
Long-term Purchase Commitment [Line Items]
Approved amount of electric power capacity (in megawatts)	431
IPL [Member] | DAEC [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	1,538	[1],[2]
IPL [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	1	[1]
IPL [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	153
IPL [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	127	[3]
IPL [Member] | SO2 emission allowances [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	34	[4]	34
IPL [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	6	[5]
IPL [Member] | 2015 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	306
IPL [Member] | 2015 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	119	[1]
IPL [Member] | 2015 [Member] | DAEC [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	119	[1],[2]
IPL [Member] | 2015 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[1]
IPL [Member] | 2015 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	108
IPL [Member] | 2015 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	61	[3]
IPL [Member] | 2015 [Member] | SO2 emission allowances [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	12	[4]
IPL [Member] | 2015 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	6	[5]
IPL [Member] | 2016 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	207
IPL [Member] | 2016 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	126	[1]
IPL [Member] | 2016 [Member] | DAEC [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	125	[1],[2]
IPL [Member] | 2016 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	1	[1]
IPL [Member] | 2016 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	32
IPL [Member] | 2016 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	35	[3]
IPL [Member] | 2016 [Member] | SO2 emission allowances [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	14	[4]
IPL [Member] | 2016 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[5]
IPL [Member] | 2017 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	171
IPL [Member] | 2017 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	138	[1]
IPL [Member] | 2017 [Member] | DAEC [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	138	[1],[2]
IPL [Member] | 2017 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[1]
IPL [Member] | 2017 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	5
IPL [Member] | 2017 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	20	[3]
IPL [Member] | 2017 [Member] | SO2 emission allowances [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	8	[4]
IPL [Member] | 2017 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[5]
IPL [Member] | 2018 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	144
IPL [Member] | 2018 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	131	[1]
IPL [Member] | 2018 [Member] | DAEC [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	131	[1],[2]
IPL [Member] | 2018 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[1]
IPL [Member] | 2018 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	2
IPL [Member] | 2018 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	11	[3]
IPL [Member] | 2018 [Member] | SO2 emission allowances [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[4]
IPL [Member] | 2018 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[5]
IPL [Member] | 2019 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	145
IPL [Member] | 2019 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	143	[1]
IPL [Member] | 2019 [Member] | DAEC [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	143	[1],[2]
IPL [Member] | 2019 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[1]
IPL [Member] | 2019 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	2
IPL [Member] | 2019 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[3]
IPL [Member] | 2019 [Member] | SO2 emission allowances [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[4]
IPL [Member] | 2019 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[5]
IPL [Member] | Thereafter [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	886
IPL [Member] | Thereafter [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	882	[1]
IPL [Member] | Thereafter [Member] | DAEC [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	882	[1],[2]
IPL [Member] | Thereafter [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[1]
IPL [Member] | Thereafter [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	4
IPL [Member] | Thereafter [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[3]
IPL [Member] | Thereafter [Member] | SO2 emission allowances [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[4]
IPL [Member] | Thereafter [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[5]
WPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	499
WPL [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	207	[1]
WPL [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	125
WPL [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	164	[3]
WPL [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	3	[5]
WPL [Member] | 2015 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	206
WPL [Member] | 2015 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	74	[1]
WPL [Member] | 2015 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	67
WPL [Member] | 2015 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	63	[3]
WPL [Member] | 2015 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	2	[5]
WPL [Member] | 2016 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	126
WPL [Member] | 2016 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	45	[1]
WPL [Member] | 2016 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	37
WPL [Member] | 2016 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	43	[3]
WPL [Member] | 2016 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	1	[5]
WPL [Member] | 2017 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	89
WPL [Member] | 2017 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	44	[1]
WPL [Member] | 2017 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	18
WPL [Member] | 2017 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	27	[3]
WPL [Member] | 2017 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[5]
WPL [Member] | 2018 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	70
WPL [Member] | 2018 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	44	[1]
WPL [Member] | 2018 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	3
WPL [Member] | 2018 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	23	[3]
WPL [Member] | 2018 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[5]
WPL [Member] | 2019 [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	8
WPL [Member] | 2019 [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[1]
WPL [Member] | 2019 [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0
WPL [Member] | 2019 [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	8	[3]
WPL [Member] | 2019 [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[5]
WPL [Member] | Thereafter [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0
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	0
WPL [Member] | Thereafter [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[3]
WPL [Member] | Thereafter [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	0	[5]
Alliant Energy and IPL [Member] | SO2 emission allowances [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments				$ 34

[1] Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased. Refer to Note 18 for additional information on purchased power transactions.

[2] Includes commitments incurred under a PPA, which grants IPL rights to purchase up to 431 MWs of capacity and the resulting energy from DAEC for a term through December 31, 2025. If energy delivered is less than the targeted energy amount, an adjustment payment will be made to IPL, which will be reflected in IPL’s fuel adjustment clause.

[3] 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, 2014 regarding expected future usage, which is subject to change.

[4] Refer to Note 2 for discussion of $34 million of charges recognized by Alliant Energy and IPL in 2011 for forward contracts to purchase SO2 emission allowances.

[5] Includes individual commitments incurred during the normal course of business that exceeded $1 million at December 31, 2014.