Consolidated Statements Of Cash Flows (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash flows from operating activities:
Net income	$ 393.3	$ 376.2	$ 335.7
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	388.1	370.9	332.9
Other amortizations	54.2	40.2	55.0
Deferred tax expense (benefit) and investment tax credits	55.2	108.3	143.3
Equity (income) loss from unconsolidated investments, net	(40.4)	(43.7)	(41.3)
Distributions from equity method investments	36.4	35.4	34.2
Equity component of allowance for funds used during construction	(23.1)	(20.3)	(14.1)
Other	2.0	(3.7)	0.7
Other changes in assets and liabilities:
Accounts receivable	48.7	(49.2)	61.3
Sales of accounts receivable	(7.0)	(101.0)	(10.0)
Regulatory assets	(439.8)	140.5	(178.1)
Regulatory liabilities	10.8	(90.8)	16.4
Deferred income taxes	138.4	101.9	69.7
Pension and other benefit obligations	215.1	(157.4)	51.3
Other	59.7	23.7	(15.9)
Net cash flows from operating activities	891.6	731.0	841.1
Cash flows used for investing activities:
Utility business - purchase of Riverside Energy Center	0	0	(403.5)
Utility business - other	(838.9)	(731.6)	(622.0)
Alliant Energy Corporate Services, Inc. and non-regulated businesses	(63.9)	(66.7)	(132.6)
Proceeds from Franklin County wind project cash grant	0	62.4	0
Other	(14.9)	(18.8)	2.6
Net cash flows used for investing activities	(917.7)	(754.7)	(1,155.5)
Cash flows from (used for) financing activities:
Common stock dividends	(225.8)	(208.3)	(199.3)
Preferred dividends paid by subsidiaries	(10.2)	(11.4)	(15.9)
Payments to redeem cumulative preferred stock	0	(211.0)	0
Proceeds from issuance of cumulative preferred stock of IPL	0	200.0	0
Proceeds from issuance of long-term debt	812.9	250.0	385.0
Payments to retire long-term debt	(358.5)	(1.5)	(1.4)
Net change in commercial paper	(138.1)	11.9	164.7
Other	(7.1)	(17.4)	(8.9)
Net cash flows from (used for) financing activities	73.2	12.3	324.2
Net increase (decrease) in cash and cash equivalents	47.1	(11.4)	9.8
Cash and cash equivalents at beginning of period	9.8	21.2	11.4
Cash and cash equivalents at end of period	56.9	9.8	21.2
Supplemental cash flows information:
Interest, net of capitalized interest	(180.8)	(171.7)	(155.2)
Income taxes, net	5.3	9.6	20.3
Significant non-cash investing and financing activities:
Accrued capital expenditures	160.3	103.8	105.3
IPL [Member]
Cash flows from operating activities:
Net income	194.6	189.9	150.2
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	197.5	191.1	188.9
Deferred tax expense (benefit) and investment tax credits	(9.7)	4.2	19.3
Equity component of allowance for funds used during construction	(17.1)	(13.8)	(5.2)
Other	11.3	(0.7)	10.6
Other changes in assets and liabilities:
Accounts receivable	43.3	(55.9)	(0.7)
Sales of accounts receivable	(7.0)	(101.0)	(10.0)
Regulatory assets	(272.9)	71.4	(129.0)
Regulatory liabilities	(18.9)	(82.3)	(12.1)
Deferred income taxes	140.4	92.4	64.6
Pension and other benefit obligations	93.8	(74.3)	21.0
Other	50.8	11.6	(6.6)
Net cash flows from operating activities	406.1	232.6	291.0
Cash flows used for investing activities:
Utility business - other	(526.0)	(400.2)	(307.5)
Other	(26.7)	(23.1)	(23.7)
Net cash flows used for investing activities	(552.7)	(423.3)	(331.2)
Cash flows from (used for) financing activities:
Common stock dividends	(140.0)	(128.1)	(122.9)
Preferred dividends paid by subsidiaries	(10.2)	(10.8)	(12.6)
Capital contributions from parent	90.0	120.0	110.0
Payments to redeem cumulative preferred stock	0	(150.0)	0
Proceeds from issuance of cumulative preferred stock of IPL	0	200.0	0
Proceeds from issuance of long-term debt	250.0	250.0	0
Payments to retire long-term debt	(38.4)	0	0
Net change in commercial paper	0	(76.3)	69.2
Other	(3.9)	(14.2)	(1.1)
Net cash flows from (used for) financing activities	147.5	190.6	42.6
Net increase (decrease) in cash and cash equivalents	0.9	(0.1)	2.4
Cash and cash equivalents at beginning of period	4.4	4.5	2.1
Cash and cash equivalents at end of period	5.3	4.4	4.5
Supplemental cash flows information:
Interest, net of capitalized interest	(89.8)	(80.7)	(78.3)
Income taxes, net	20.1	0.1	(3.3)
Significant non-cash investing and financing activities:
Accrued capital expenditures	113.2	58.1	53.4
WPL [Member]
Cash flows from operating activities:
Net income	180.8	177.5	165.7
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	181.2	172.2	140.9
Other amortizations	47.3	29.5	43.7
Deferred tax expense (benefit) and investment tax credits	80.7	86.5	88.6
Equity (income) loss from unconsolidated investments, net	(42.8)	(43.7)	(42.1)
Distributions from equity method investments	36.4	35.4	34.2
Equity component of allowance for funds used during construction	(6.0)	(6.5)	(8.9)
Other	(1.2)	(0.2)	(2.9)
Other changes in assets and liabilities:
Regulatory assets	(166.9)	69.1	(49.1)
Regulatory liabilities	29.7	(8.5)	28.5
Accrued taxes	0.1	(26.9)	19.2
Pension and other benefit obligations	92.0	(71.3)	31.7
Other	(6.9)	10.2	(22.1)
Net cash flows from operating activities	424.4	423.3	427.4
Cash flows used for investing activities:
Utility business - purchase of Riverside Energy Center	0	0	(403.5)
Utility business - other	(312.9)	(331.4)	(314.5)
Other	(7.2)	(4.5)	7.8
Net cash flows used for investing activities	(320.1)	(335.9)	(710.2)
Cash flows from (used for) financing activities:
Common stock dividends	(118.7)	(116.3)	(112.0)
Preferred dividends paid by subsidiaries	0	(0.6)	(3.3)
Capital contributions from parent	0	0	90.0
Payments to redeem cumulative preferred stock	0	(61.0)	0
Proceeds from issuance of long-term debt	250.0	0	250.0
Net change in commercial paper	(183.7)	97.1	60.9
Other	(5.7)	(6.8)	(4.8)
Net cash flows from (used for) financing activities	(58.1)	(87.6)	280.8
Net increase (decrease) in cash and cash equivalents	46.2	(0.2)	(2.0)
Cash and cash equivalents at beginning of period	0.5	0.7	2.7
Cash and cash equivalents at end of period	46.7	0.5	0.7
Supplemental cash flows information:
Interest, net of capitalized interest	(84.6)	(85.0)	(79.5)
Income taxes, net	(12.2)	(22.9)	3.3
Significant non-cash investing and financing activities:
Accrued capital expenditures	$ 38.4	$ 37.7	$ 39.5