Consolidated Statements Of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cash flows from operating activities:
Net income	$ 388.4	$ 393.3	$ 376.2
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	401.3	388.1	370.9
Other amortizations	12.4	54.2	40.2
Deferred tax expense (benefit) and investment tax credits	114.2	55.2	108.3
Equity (income) loss from unconsolidated investments, net	(33.8)	(40.4)	(43.7)
Distributions from equity method investments	30.6	36.4	35.4
Equity component of allowance for funds used during construction	(24.4)	(23.1)	(20.3)
Other	15.7	2.0	(3.7)
Other changes in assets and liabilities:
Accounts receivable	36.8	48.7	(49.2)
Sales of accounts receivable	(17.0)	(7.0)	(101.0)
Regulatory assets	(104.5)	(439.8)	140.5
Regulatory liabilities	(67.8)	10.8	(90.8)
Deferred taxes	94.6	138.4	101.9
Pension and other benefit obligations	30.1	215.1	(157.4)
Other	(5.4)	59.7	23.7
Net cash flows from operating activities	871.2	891.6	731.0
Cash flows used for investing activities:
Utility business construction and acquisition expenditures	(963.6)	(838.9)	(731.6)
Alliant Energy Corporate Services, Inc. and non-regulated businesses construction and acquisition expenditures	(70.7)	(63.9)	(66.7)
Proceeds from Minnesota electric and natural gas distribution asset sales	139.9	0.0	0.0
Proceeds from Franklin County wind farm cash grant	0.0	0.0	62.4
Other	(24.8)	(14.9)	(18.8)
Net cash flows used for investing activities	(919.2)	(917.7)	(754.7)
Cash flows from (used for) financing activities:
Common stock dividends	(247.3)	(225.8)	(208.3)
Proceeds from issuance of common stock, net	151.2	0.0	0.0
Payments to redeem cumulative preferred stock of subsidiaries	0.0	0.0	(211.0)
Proceeds from issuance of cumulative preferred stock of IPL	0.0	0.0	200.0
Proceeds from issuance of long-term debt	250.7	812.9	250.0
Payments to retire long-term debt	(183.0)	(358.5)	(1.5)
Net change in commercial paper	18.5	(138.1)	11.9
Other	6.8	(17.3)	(28.8)
Net cash flows from (used for) financing activities	(3.1)	73.2	12.3
Net increase (decrease) in cash and cash equivalents	(51.1)	47.1	(11.4)
Cash and cash equivalents at beginning of period	56.9	9.8	21.2
Cash and cash equivalents at end of period	5.8	56.9	9.8
Supplemental cash flows information:
Interest, net of capitalized interest	(184.8)	(180.8)	(171.7)
Income taxes, net	0.0	5.3	9.6
Significant non-cash investing and financing activities:
Accrued capital expenditures	148.3	160.3	103.8
IPL [Member]
Cash flows from operating activities:
Net income	196.2	191.8	188.3
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	207.2	197.5	191.1
Deferred tax expense (benefit) and investment tax credits	28.9	(11.5)	3.0
Equity component of allowance for funds used during construction	(18.6)	(17.1)	(13.8)
Other	19.5	11.3	(0.7)
Other changes in assets and liabilities:
Accounts receivable	20.4	43.3	(55.9)
Sales of accounts receivable	(17.0)	(7.0)	(101.0)
Regulatory assets	(76.3)	(272.9)	71.4
Accounts payable	(42.7)	18.8	25.6
Regulatory liabilities	(75.5)	(18.9)	(82.3)
Deferred taxes	82.1	140.4	92.4
Pension and other benefit obligations	17.8	93.8	(74.3)
Other	43.0	36.6	(11.2)
Net cash flows from operating activities	385.0	406.1	232.6
Cash flows used for investing activities:
Utility business construction and acquisition expenditures	(619.3)	(526.0)	(400.2)
Proceeds from Minnesota electric and natural gas distribution asset sales	139.9	0.0	0.0
Other	(32.5)	(26.7)	(23.1)
Net cash flows used for investing activities	(511.9)	(552.7)	(423.3)
Cash flows from (used for) financing activities:
Common stock dividends	(140.0)	(140.0)	(128.1)
Capital contributions from parent	165.0	90.0	120.0
Payments to redeem cumulative preferred stock of subsidiaries	0.0	0.0	(150.0)
Proceeds from issuance of cumulative preferred stock of IPL	0.0	0.0	200.0
Proceeds from issuance of long-term debt	250.0	250.0	250.0
Payments to retire long-term debt	(150.0)	(38.4)	0.0
Net change in commercial paper	0.0	0.0	(76.3)
Other	1.1	(14.1)	(25.0)
Net cash flows from (used for) financing activities	126.1	147.5	190.6
Net increase (decrease) in cash and cash equivalents	(0.8)	0.9	(0.1)
Cash and cash equivalents at beginning of period	5.3	4.4	4.5
Cash and cash equivalents at end of period	4.5	5.3	4.4
Supplemental cash flows information:
Interest, net of capitalized interest	(93.9)	(89.8)	(80.7)
Income taxes, net	19.3	20.1	0.1
Significant non-cash investing and financing activities:
Accrued capital expenditures	77.0	113.2	58.1
WPL [Member]
Cash flows from operating activities:
Net income	177.6	181.1	179.1
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	184.3	181.2	172.2
Other amortizations	5.3	47.3	29.5
Deferred tax expense (benefit) and investment tax credits	77.6	82.6	89.8
Equity (income) loss from unconsolidated investments, net	(35.1)	(42.8)	(43.7)
Distributions from equity method investments	30.6	36.4	35.4
Other	(5.7)	(7.2)	(6.7)
Other changes in assets and liabilities:
Regulatory assets	(28.2)	(166.9)	69.1
Regulatory liabilities	7.7	29.7	(8.5)
Pension and other benefit obligations	8.3	92.0	(71.3)
Other	27.4	(9.0)	(21.6)
Net cash flows from operating activities	449.8	424.4	423.3
Cash flows used for investing activities:
Utility business construction and acquisition expenditures	(344.3)	(312.9)	(331.4)
Other	(13.9)	(7.2)	(4.5)
Net cash flows used for investing activities	(358.2)	(320.1)	(335.9)
Cash flows from (used for) financing activities:
Common stock dividends	(126.9)	(118.7)	(116.3)
Payments to redeem cumulative preferred stock of subsidiaries	0.0	0.0	(61.0)
Proceeds from issuance of long-term debt	0.0	250.0	0.0
Net change in commercial paper	19.9	(183.7)	97.1
Other	(30.9)	(5.7)	(7.4)
Net cash flows from (used for) financing activities	(137.9)	(58.1)	(87.6)
Net increase (decrease) in cash and cash equivalents	(46.3)	46.2	(0.2)
Cash and cash equivalents at beginning of period	46.7	0.5	0.7
Cash and cash equivalents at end of period	0.4	46.7	0.5
Supplemental cash flows information:
Interest, net of capitalized interest	(93.1)	(84.6)	(85.0)
Income taxes, net	(7.4)	(12.2)	(22.9)
Significant non-cash investing and financing activities:
Accrued capital expenditures	$ 55.2	$ 38.4	$ 37.7