Condensed Consolidated Statements Of Cash Flows (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Cash flows from operating activities:
Net income	$ 110.6	$ 80.1
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	95.5	92.6
Other amortizations	15.1	9.7
Deferred taxes and investment tax credits	35.9	22.5
Equity income from unconsolidated investments, net	(11.4)	(10.7)
Distributions from equity method investments	9.4	8.9
Other	(7.2)	(3.6)
Other changes in assets and liabilities:
Accounts receivable	(55.6)	(12.9)
Sales of accounts receivable	46.0	(30.0)
Production fuel	34.8	3.3
Gas stored underground	28.5	28.7
Regulatory assets	(20.7)	19.9
Accounts payable	25.4	1.5
Derivative liabilities	(11.8)	(23.3)
Other	(0.9)	11.9
Net cash flows from operating activities	293.6	198.6
Cash flows used for investing activities:
Utility construction and acquisition expenditures	(159.0)	(153.2)
Alliant Energy Corporate Services, Inc. and non-regulated businesses construction and acquisition expenditures	(14.0)	(14.1)
Proceeds from Franklin County wind project cash grant	0	62.4
Other	(3.8)	(14.8)
Net cash flows used for investing activities	(176.8)	(119.7)
Cash flows from (used for) financing activities:
Common stock dividends	(56.5)	(52.2)
Preferred dividends paid by subsidiaries	(2.6)	(3.8)
Payments to redeem cumulative preferred stock	0	(211.0)
Proceeds from issuance of cumulative preferred stock	0	200.0
Net change in commercial paper	(58.1)	10.9
Other	5.1	9.4
Net cash flows from (used for) financing activities	(112.1)	(46.7)
Net increase (decrease) in cash and cash equivalents	4.7	32.2
Cash and cash equivalents at beginning of period	9.8	21.2
Cash and cash equivalents at end of period	14.5	53.4
Supplemental cash flows information:
Interest, net of capitalized interest	41.4	43.5
Income taxes, net of refunds	(3.9)	2.3
Significant non-cash investing and financing activities:
Accrued capital expenditures	85.9	99.5
IPL [Member]
Cash flows from operating activities:
Net income	46.0	31.5
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	48.7	47.6
Deferred taxes and investment tax credits	12.4	(10.7)
Other	(2.3)	(0.7)
Other changes in assets and liabilities:
Accounts receivable	(48.9)	(34.7)
Sales of accounts receivable	46.0	(30.0)
Production fuel	21.0	0.8
Accounts payable	28.8	8.1
Accounts payable to associated companies	(28.8)	8.1
Regulatory liabilities	(9.0)	14.7
Deferred income taxes	20.3	23.4
Other	(28.6)	7.1
Net cash flows from operating activities	105.6	65.2
Cash flows used for investing activities:
Utility construction and acquisition expenditures	(91.1)	(77.5)
Other	(5.5)	(5.7)
Net cash flows used for investing activities	(96.6)	(83.2)
Cash flows from (used for) financing activities:
Common stock dividends	(35.0)	(31.6)
Preferred dividends paid by subsidiaries	(2.6)	(3.2)
Capital contributions from parent	30.0	30.0
Payments to redeem cumulative preferred stock	0	(150.0)
Proceeds from issuance of cumulative preferred stock	0	200.0
Net change in commercial paper	0	(41.3)
Other	0	14.3
Net cash flows from (used for) financing activities	(7.6)	18.2
Net increase (decrease) in cash and cash equivalents	1.4	0.2
Cash and cash equivalents at beginning of period	4.4	4.5
Cash and cash equivalents at end of period	5.8	4.7
Supplemental cash flows information:
Interest, net of capitalized interest	19.3	21.1
Income taxes, net of refunds	1.5	4.8
Significant non-cash investing and financing activities:
Accrued capital expenditures	46.3	60.7
WPL [Member]
Cash flows from operating activities:
Net income	54.8	43.6
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	44.7	43.1
Other amortizations	12.8	7.1
Deferred taxes and investment tax credits	20.8	26.7
Equity income from unconsolidated investments, net	(11.4)	(10.8)
Distributions from equity method investments	9.4	8.9
Other	(2.1)	(1.3)
Other changes in assets and liabilities:
Regulatory assets	(10.9)	13.3
Derivative assets	(19.8)	(2.4)
Accrued taxes	5.4	(24.3)
Regulatory liabilities	26.1	5.8
Other	(1.1)	(4.3)
Net cash flows from operating activities	128.7	105.4
Cash flows used for investing activities:
Utility construction and acquisition expenditures	(67.9)	(75.7)
Other	(2.6)	(0.4)
Net cash flows used for investing activities	(70.5)	(76.1)
Cash flows from (used for) financing activities:
Common stock dividends	(29.7)	(29.1)
Payments to redeem cumulative preferred stock	0	(61.0)
Net change in commercial paper	(28.2)	73.4
Other	4.1	(4.9)
Net cash flows from (used for) financing activities	(53.8)	(21.6)
Net increase (decrease) in cash and cash equivalents	4.4	7.7
Cash and cash equivalents at beginning of period	0.5	0.7
Cash and cash equivalents at end of period	4.9	8.4
Supplemental cash flows information:
Interest, net of capitalized interest	23.2	23.4
Income taxes, net of refunds	(0.6)	25.9
Significant non-cash investing and financing activities:
Accrued capital expenditures	$ 33.7	$ 35.0