XML 55 R32.htm IDEA: XBRL DOCUMENT
v3.8.0.1

Commitments And Contingencies (Tables) | 3 Months Ended
--- | ---
Mar. 31, 2018
Commitments and Contingencies [Line Items] |
Other Purchase Obligations | At March 31, 2018, minimum future commitments related to these purchase obligations were as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
Purchased power (a) |  | $1,175 |  |  |  | $1,127 |  |  |  | $48 |
Natural gas | 892 |  |  | 362 |  |  | 530 |
Coal (b) | 165 |  |  | 88 |  |  | 77 |
Other (c) | 46 |  |  | 26 |  |  | 6 |
|  | $2,278 |  |  |  | $1,603 |  |  |  | $661 |
(a) | Includes payments required by purchased power agreements for capacity rights and minimum quantities of MWhs required to be purchased.
(b) | 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 March 31, 2018 regarding expected future usage, which is subject to change.
(c) | Includes individual commitments incurred during the normal course of business that exceeded $1 million at March 31, 2018.
MGP Site Estimated Future Costs And Recorded Liabilities | At March 31, 2018, estimated future costs expected to be incurred for the investigation, remediation and monitoring of the MGP sites, as well as environmental liabilities recorded on the balance sheets for these sites, which are not discounted, were as follows (in millions). At March 31, 2018, such amounts for WPL were not material.
| Alliant Energy |  | IPL
Range of estimated future costs |  | $11 |  | - | $30 |  |  | $9 |  | - | $25
Current and non-current environmental liabilities | 16 |  | 13
IPL [Member] |
Commitments and Contingencies [Line Items] |
Other Purchase Obligations | At March 31, 2018, minimum future commitments related to these purchase obligations were as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
Purchased power (a) |  | $1,175 |  |  |  | $1,127 |  |  |  | $48 |
Natural gas | 892 |  |  | 362 |  |  | 530 |
Coal (b) | 165 |  |  | 88 |  |  | 77 |
Other (c) | 46 |  |  | 26 |  |  | 6 |
|  | $2,278 |  |  |  | $1,603 |  |  |  | $661 |
(a) | Includes payments required by purchased power agreements for capacity rights and minimum quantities of MWhs required to be purchased.
(b) | 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 March 31, 2018 regarding expected future usage, which is subject to change.
(c) | Includes individual commitments incurred during the normal course of business that exceeded $1 million at March 31, 2018.
MGP Site Estimated Future Costs And Recorded Liabilities | At March 31, 2018, estimated future costs expected to be incurred for the investigation, remediation and monitoring of the MGP sites, as well as environmental liabilities recorded on the balance sheets for these sites, which are not discounted, were as follows (in millions). At March 31, 2018, such amounts for WPL were not material.
| Alliant Energy |  | IPL
Range of estimated future costs |  | $11 |  | - | $30 |  |  | $9 |  | - | $25
Current and non-current environmental liabilities | 16 |  | 13
WPL [Member] |
Commitments and Contingencies [Line Items] |
Other Purchase Obligations | At March 31, 2018, minimum future commitments related to these purchase obligations were as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
Purchased power (a) |  | $1,175 |  |  |  | $1,127 |  |  |  | $48 |
Natural gas | 892 |  |  | 362 |  |  | 530 |
Coal (b) | 165 |  |  | 88 |  |  | 77 |
Other (c) | 46 |  |  | 26 |  |  | 6 |
|  | $2,278 |  |  |  | $1,603 |  |  |  | $661 |
(a) | Includes payments required by purchased power agreements for capacity rights and minimum quantities of MWhs required to be purchased.
(b) | 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 March 31, 2018 regarding expected future usage, which is subject to change.
(c) | Includes individual commitments incurred during the normal course of business that exceeded $1 million at March 31, 2018.

X
- Definition Long-Term Purchase Commitment, Operating Expenses Purchase Obligation [Table Text Block] + References No definition available. + Details
Name: | lnt_LongTermPurchaseCommitmentOperatingExpensesPurchaseObligationTableTextBlock
Namespace Prefix: | lnt_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- Definition Tabular disclosure of material liabilities for remediation, site restoration, postclosure, monitoring commitments, or other exit costs that may occur on the sale, disposal or abandonment of a property as a result of unanticipated contamination of the assets. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 5.Y.Q4) -URI http://asc.fasb.org/extlink&oid=27011672&loc=d3e149879-122751 + Details
Name: | us-gaap_EnvironmentalExitCostsByCostTextBlock
Namespace Prefix: | us-gaap_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_LongTermPurchaseCommitmentLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | dei_LegalEntityAxis=lnt_IplMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | dei_LegalEntityAxis=lnt_WplMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |