Consolidated Statements Of Cash Flows (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Cash flows from operating activities:
Net income	$ 321.9	$ 306.3	$ 129.7
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	323.8	292.3	275.6
Depreciation and amortization	323.8	291.3	273.6
Other amortizations	56.3	51.8	42.1
Deferred tax expense and investment tax credits	10.2	216.6	94.3
Loss on early extinguishment of debt			203.0
Equity (income)/loss from unconsolidated investments, net	(39.3)	(38.1)	(36.6)
Distributions from equity method investments	32.3	32.2	29.9
Equity component of allowance for funds used during construction	(7.6)	(11.2)	(28.2)
Non-cash valuation and regulated-related charges	25.5	38.0	20.4
Other	(5.2)	(4.7)	(5.7)
Other changes in assets and liabilities:
Accounts receivable	(54.3)	16.3	73.5
Sales of accounts receivable	75.0	65.0	(25.0)
Income tax refunds receivable	0.3	130.4	(102.3)
Production fuel	22.5	17.4	(28.5)
Regulatory assets	(413.1)	(20.8)	(163.9)
Regulatory liabilities	168.3	8.4	136.7
Accrued taxes	2.0	(32.4)	25.8
Derivative liabilities	10.7	(52.0)	16.3
Deferred income taxes	148.5	28.9	118.9
Non-current taxes payable	(5.1)	(66.6)	60.7
Pension and other benefit obligations	8.9	(20.1)	(190.0)
Other	21.1	27.2	10.4
Net cash flows from operating activities	702.7	984.9	657.1
Cash flows used for investing activities:
Utility business	(608.1)	(833.3)	(1,149.6)
Non-regulated businesses	(65.3)	(33.6)	(53.0)
Advances for customer energy efficiency projects	(5.1)	(17.1)	(31.0)
Collections of advances for customer energy efficiency projects	31.0	34.2	63.6
Insurance proceeds received for property damages			37.7
Other	(4.6)	(16.7)	(16.6)
Net cash flows used for investing activities	(652.1)	(866.5)	(1,148.9)
Cash flows from (used for) financing activities:
Common stock dividends	(188.1)	(174.6)	(165.5)
Preferred dividends paid by subsidiaries	(16.8)	(18.7)	(18.7)
Payments to redeem cumulative preferred stock	(40.0)
Proceeds from issuance of long-term debt	0.4	500.0	800.2
Payments to retire long-term debt	(1.3)	(307.8)	(377.9)
Net change in short-term borrowings	55.4	(142.6)	103.9
Other	(8.1)	9.3	(21.8)
Net cash flows from (used for) financing activities	(198.5)	(134.4)	320.2
Net decrease in cash and cash equivalents	(147.9)	(16.0)	(171.6)
Cash and cash equivalents at beginning of period	159.3	175.3	346.9
Cash and cash equivalents at end of period	11.4	159.3	175.3
Supplemental cash flows information:
Interest, net of capitalized interest	157.6	165.5	142.4
Income taxes, net of refunds	(10.8)	(116.2)	(140.7)
Significant noncash investing and financing activities:
Accrued capital expenditures	49.7	75.0	66.7
IPL [Member]
Cash flows from operating activities:
Net income	139.3	143.4	153.0
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	179.1	177.0	152.8
Deferred tax expense and investment tax credits	(58.6)	116.0	73.3
Equity component of allowance for funds used during construction	(3.5)	(3.0)	(24.2)
Non-cash valuation and regulated-related charges	14.8	30.5	8.0
Other	8.7	3.7	(1.3)
Other changes in assets and liabilities:
Accounts receivable	22.4	5.1	40.6
Sales of accounts receivable	75.0	65.0	(25.0)
Income tax refunds receivable	(9.3)	84.3	(54.8)
Production fuel	12.4	21.0	(31.1)
Regulatory assets	(328.8)	(49.5)	(109.7)
Regulatory liabilities	156.3	17.5	158.9
Accrued taxes	(18.6)	(5.9)	21.9
Derivative liabilities	9.6	(29.0)	(35.2)
Deferred income taxes	145.9	42.0	116.5
Non-current taxes payable	(4.8)	(28.4)	25.8
Pension and other benefit obligations	(8.3)	(9.0)	(94.7)
Other	35.3	(31.1)	(1.6)
Net cash flows from operating activities	366.9	549.6	373.2
Cash flows used for investing activities:
Utility business	(293.7)	(382.8)	(733.6)
Proceeds from sale of wind project assets to affiliate	115.3
Insurance proceeds received for property damages			37.7
Other	(22.2)	(32.2)	(16.8)
Net cash flows used for investing activities	(200.6)	(415.0)	(712.7)
Cash flows from (used for) financing activities:
Common stock dividends	(73.4)
Preferred dividends paid by subsidiaries	(13.5)	(15.4)	(15.4)
Capital contributions from parent	54.0	50.0	150.0
Repayment of capital to parent	(100.7)	(118.2)	(106.1)
Payments to redeem cumulative preferred stock	(40.0)
Proceeds from issuance of long-term debt		350.0	300.0
Payments to retire long-term debt		(206.3)	(135.0)
Net change in short-term borrowings	7.1	(190.0)	147.6
Other	(3.4)	0.6	(7.4)
Net cash flows from (used for) financing activities	(169.9)	(129.3)	333.7
Net decrease in cash and cash equivalents	(3.6)	5.3	(5.8)
Cash and cash equivalents at beginning of period	5.7	0.4	6.2
Cash and cash equivalents at end of period	2.1	5.7	0.4
Supplemental cash flows information:
Interest, net of capitalized interest	78.0	82.0	70.3
Income taxes, net of refunds	25.3	(125.9)	(87.5)
Significant noncash investing and financing activities:
Accrued capital expenditures	23.9	45.7	56.2
WPL [Member]
Cash flows from operating activities:
Net income	163.5	152.3	89.5
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	140.1	108.6	115.4
Other amortizations	42.4	39.5	35.2
Deferred tax expense and investment tax credits	93.7	98.5	157.7
Equity (income)/loss from unconsolidated investments, net	(38.7)	(37.8)	(37.0)
Distributions from equity method investments	32.3	32.2	29.9
Equity component of allowance for funds used during construction	(4.1)	(8.2)	(4.0)
Non-cash valuation and regulated-related charges	10.8		12.5
Other changes in assets and liabilities:
Accounts receivable	9.8	4.6	31.3
Income tax refunds receivable	39.9	40.7	(72.9)
Regulatory assets	(84.3)	28.7	(54.2)
Regulatory liabilities	12.0	(9.1)	(22.2)
Derivative liabilities	1.1	(23.0)	51.5
Non-current taxes payable	(0.3)	(38.5)	36.2
Pension and other benefit obligations	8.8	(2.5)	(63.4)
Other	1.8	(13.6)	0.3
Net cash flows from operating activities	428.8	372.4	305.8
Cash flows used for investing activities:
Other utility business	(314.4)	(450.5)	(416.0)
Advances for customer energy efficiency projects	(5.1)	(16.0)	(28.1)
Collections of advances for customer energy efficiency projects	26.8	30.3	58.6
Other	(12.7)	(13.1)	(15.5)
Net cash flows used for investing activities	(305.4)	(449.3)	(493.4)
Cash flows from (used for) financing activities:
Common stock dividends	(112.1)	(109.5)	(91.0)
Preferred dividends paid by subsidiaries	(3.3)	(3.3)	(3.3)
Capital contributions from parent	25.0	75.0	100.0
Proceeds from issuance of long-term debt		150.0	250.0
Payments to retire long-term debt		(100.0)
Net change in short-term borrowings	(21.7)	47.4	(43.7)
Other	(8.7)	(1.1)	(10.4)
Net cash flows from (used for) financing activities	(120.8)	58.5	201.6
Net decrease in cash and cash equivalents	2.6	(18.4)	14.0
Cash and cash equivalents at beginning of period	0.1	18.5	4.5
Cash and cash equivalents at end of period	2.7	0.1	18.5
Supplemental cash flows information:
Interest, net of capitalized interest	79.9	80.9	69.6
Income taxes, net of refunds	(51.3)	(3.8)	(76.1)
Significant noncash investing and financing activities:
Accrued capital expenditures	19.7	27.4	16.4
Neenah Energy Facility [Member] | WPL [Member]
Cash flows used for investing activities:
Utility construction and acquisition			$ 92.4