XML 58 R38.htm IDEA: XBRL DOCUMENT
v3.19.2

Summary Of Significant Accounting Policies (Narrative) (Details) - USD ($) $ in Millions | 6 Months Ended |
--- | --- | ---
Jun. 30, 2019 | Jun. 30, 2018 | Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |
Money market fund investments | $ 161.8 |  | $ 0.0
Money market fund investments interest rate, percentage | 2.40% |  |
Increase in operating cash flows from change in method of presentation to daily transactional activity |  | $ 339.4 |
Net cash flows from operating activities | $ 276.9 | 274.4 |
IPL [Member] |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |
Increase in operating cash flows from change in method of presentation to daily transactional activity |  | 339.4 |
Net cash flows from operating activities | 89.0 | 12.8 |
WPL [Member] |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |
Money market fund investments | $ 160.4 |  | $ 0.0
Money market fund investments interest rate, percentage | 2.40% |  |
Net cash flows from operating activities | $ 208.2 | $ 225.9 |

X
- Definition Change In Method Of Calculation + References No definition available. + Details
Name: | lnt_ChangeInMethodOfCalculation
Namespace Prefix: | lnt_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Investment in short-term money-market instruments (such as commercial paper, banker's acceptances, repurchase agreements, government securities, certificates of deposit, and so forth) which are highly liquid (that is, readily convertible to known amounts of cash) and so near their maturity that they present an insignificant risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify as cash equivalents by definition. Original maturity means an original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months. + References No definition available. + Details
Name: | us-gaap_MoneyMarketFundsAtCarryingValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of cash inflow (outflow) from operating activities, including discontinued operations. Operating activity cash flows include transactions, adjustments, and changes in value not defined as investing or financing activities. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 25 -URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3536-108585 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 24 -URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3521-108585 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585 + Details
Name: | us-gaap_NetCashProvidedByUsedInOperatingActivities
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
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_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The weighted average interest rate for domestic money market demand account deposit liabilities. + References No definition available. + Details
Name: | us-gaap_WeightedAverageRateDomesticDepositMoneyMarket
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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: |