Derivative Instruments (Tables)

12 Months Ended

Dec. 31, 2017

Derivative [Line Items]

Notional Amounts of Derivative Instruments

As of December 31, 2017, gross notional amounts and settlement/delivery years related to outstanding swap contracts, option contracts, physical forward contracts and FTRs that were accounted for as commodity derivative instruments were as follows (units in thousands):

	Electricity		FTRs		Natural Gas		Coal		Diesel Fuel
	MWhs	Years	MWhs	Years	Dths	Years	Tons	Years	Gallons	Years
Alliant Energy	1,314	2018	8,970	2018	170,463	2018-2026	8,177	2018-2020	6,552	2018-2019
IPL	—	—	5,886	2018	72,662	2018-2026	3,339	2018-2020	—	—
WPL	1,314	2018	3,084	2018	97,801	2018-2026	4,838	2018-2020	6,552	2018-2019

Fair Value of Financial Instruments

At December 31, the fair values of current derivative assets are included in “Other current assets,” non-current derivative assets are included in “Deferred charges and other,” current derivative liabilities are included in “Other current liabilities” and non-current derivative liabilities are included in “Other liabilities” on the balance sheets as follows (in millions):

	Alliant Energy				IPL				WPL
	2017		2016		2017		2016		2017		2016
Current derivative assets		$21.1		$29.4		$15.8		$19.1		$5.3		$10.3
Non-current derivative assets	4.0		12.0		1.3		1.7		2.7		10.3
Current derivative liabilities	18.7		13.3		5.0		2.7		13.7		10.6
Non-current derivative liabilities	23.0		15.3		14.4		5.6		8.6		9.7

IPL [Member]

Derivative [Line Items]

Notional Amounts of Derivative Instruments

As of December 31, 2017, gross notional amounts and settlement/delivery years related to outstanding swap contracts, option contracts, physical forward contracts and FTRs that were accounted for as commodity derivative instruments were as follows (units in thousands):

	Electricity		FTRs		Natural Gas		Coal		Diesel Fuel
	MWhs	Years	MWhs	Years	Dths	Years	Tons	Years	Gallons	Years
Alliant Energy	1,314	2018	8,970	2018	170,463	2018-2026	8,177	2018-2020	6,552	2018-2019
IPL	—	—	5,886	2018	72,662	2018-2026	3,339	2018-2020	—	—
WPL	1,314	2018	3,084	2018	97,801	2018-2026	4,838	2018-2020	6,552	2018-2019

Fair Value of Financial Instruments

At December 31, the fair values of current derivative assets are included in “Other current assets,” non-current derivative assets are included in “Deferred charges and other,” current derivative liabilities are included in “Other current liabilities” and non-current derivative liabilities are included in “Other liabilities” on the balance sheets as follows (in millions):

	Alliant Energy				IPL				WPL
	2017		2016		2017		2016		2017		2016
Current derivative assets		$21.1		$29.4		$15.8		$19.1		$5.3		$10.3
Non-current derivative assets	4.0		12.0		1.3		1.7		2.7		10.3
Current derivative liabilities	18.7		13.3		5.0		2.7		13.7		10.6
Non-current derivative liabilities	23.0		15.3		14.4		5.6		8.6		9.7

WPL [Member]

Derivative [Line Items]

Notional Amounts of Derivative Instruments

As of December 31, 2017, gross notional amounts and settlement/delivery years related to outstanding swap contracts, option contracts, physical forward contracts and FTRs that were accounted for as commodity derivative instruments were as follows (units in thousands):

	Electricity		FTRs		Natural Gas		Coal		Diesel Fuel
	MWhs	Years	MWhs	Years	Dths	Years	Tons	Years	Gallons	Years
Alliant Energy	1,314	2018	8,970	2018	170,463	2018-2026	8,177	2018-2020	6,552	2018-2019
IPL	—	—	5,886	2018	72,662	2018-2026	3,339	2018-2020	—	—
WPL	1,314	2018	3,084	2018	97,801	2018-2026	4,838	2018-2020	6,552	2018-2019

Fair Value of Financial Instruments

At December 31, the fair values of current derivative assets are included in “Other current assets,” non-current derivative assets are included in “Deferred charges and other,” current derivative liabilities are included in “Other current liabilities” and non-current derivative liabilities are included in “Other liabilities” on the balance sheets as follows (in millions):

	Alliant Energy				IPL				WPL
	2017		2016		2017		2016		2017		2016
Current derivative assets		$21.1		$29.4		$15.8		$19.1		$5.3		$10.3
Non-current derivative assets	4.0		12.0		1.3		1.7		2.7		10.3
Current derivative liabilities	18.7		13.3		5.0		2.7		13.7		10.6
Non-current derivative liabilities	23.0		15.3		14.4		5.6		8.6		9.7