Condensed Consolidated Statements Of Cash Flows (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012
Cash flows from operating activities:
Net income	$ 147.9	$ 108.7
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	185.3	164.3
Other amortizations	19.3	27.6
Deferred tax expense (benefit) and investment tax credits	40.8	56.3
Equity income from unconsolidated investments, net	(21.6)	(20.0)
Distributions from equity method investments	17.4	16.8
Other	(9.6)	(7.6)
Other changes in assets and liabilities:
Accounts receivable	(16.4)	54.0
Sales of accounts receivable	5.0	(27.0)
Derivative assets	(34.3)	(28.7)
Accounts payable	53.3	28.9
Regulatory liabilities	(15.1)	(43.5)
Deferred income taxes	43.4	26.7
Other	7.9	(17.3)
Net cash flows from operating activities	423.3	339.2
Cash flows used for investing activities:
Utility construction and acquisition expenditures	(341.5)	(247.3)
Alliant Energy Corporate Services, Inc. and non-regulated businesses	(27.5)	(75.1)
Proceeds from Franklin County wind project cash grant	62.4	0
Other	(15.6)	0.6
Net cash flows used for investing activities	(322.2)	(321.8)
Cash flows from (used for) financing activities:
Common stock dividends	(104.2)	(99.7)
Preferred dividends paid by subsidiaries	(6.3)	(7.9)
Payments to redeem cumulative preferred stock	(211.0)	0
Proceeds from issuance of cumulative preferred stock	200.0	0
Net change in commercial paper	10.6	110.0
Other	0.1	(0.4)
Net cash flows from (used for) financing activities	(110.8)	2.0
Net increase (decrease) in cash and cash equivalents	(9.7)	19.4
Cash and cash equivalents at beginning of period	21.2	11.4
Cash and cash equivalents at end of period	11.5	30.8
Supplemental cash flows information:
Interest, net of capitalized interest	86.7	77.4
Income taxes, net of refunds	(9.7)	(0.9)
Significant non-cash investing and financing activities:
Accrued capital expenditures	94.1	100.3
IPL [Member]
Cash flows from operating activities:
Net income	56.2	18.1
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	95.2	93.8
Deferred tax expense (benefit) and investment tax credits	(6.0)	8.2
Other	(2.7)	1.8
Other changes in assets and liabilities:
Accounts receivable	(33.7)	(0.5)
Sales of accounts receivable	5.0	(27.0)
Derivative assets	(27.6)	(20.9)
Accounts payable	51.3	13.1
Regulatory liabilities	(27.1)	(61.5)
Accrued taxes	10.4	23.4
Deferred income taxes	43.1	25.7
Other	9.6	2.2
Net cash flows from operating activities	173.7	76.4
Cash flows used for investing activities:
Utility construction and acquisition expenditures	(180.0)	(109.9)
Other	(9.8)	(10.4)
Net cash flows used for investing activities	(189.8)	(120.3)
Cash flows from (used for) financing activities:
Common stock dividends	(63.5)	(60.8)
Preferred dividends paid by subsidiaries	(5.7)	(6.2)
Capital contributions from parent	60.0	50.0
Payments to redeem cumulative preferred stock	(150.0)	0
Proceeds from issuance of cumulative preferred stock	200.0	0
Net change in commercial paper	(21.3)	58.3
Other	(2.8)	3.3
Net cash flows from (used for) financing activities	16.7	44.6
Net increase (decrease) in cash and cash equivalents	0.6	0.7
Cash and cash equivalents at beginning of period	4.5	2.1
Cash and cash equivalents at end of period	5.1	2.8
Supplemental cash flows information:
Interest, net of capitalized interest	41.5	39.2
Income taxes, net of refunds	2.2	(15.4)
Significant non-cash investing and financing activities:
Accrued capital expenditures	56.2	61.1
WPL [Member]
Cash flows from operating activities:
Net income	78.0	68.0
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	86.3	69.0
Other amortizations	14.4	21.8
Deferred tax expense (benefit) and investment tax credits	39.1	43.3
Equity income from unconsolidated investments, net	(21.6)	(20.7)
Distributions from equity method investments	17.4	16.8
Other	(3.6)	(6.5)
Other changes in assets and liabilities:
Accounts receivable	19.7	8.4
Income tax refunds receivable	1.3	(10.9)
Regulatory liabilities	12.0	18.0
Accrued taxes	(17.3)	(3.9)
Other	(0.5)	(21.4)
Net cash flows from operating activities	225.2	181.9
Cash flows used for investing activities:
Utility construction and acquisition expenditures	(161.5)	(137.4)
Other	(2.8)	4.0
Net cash flows used for investing activities	(164.3)	(133.4)
Cash flows from (used for) financing activities:
Common stock dividends	(58.2)	(56.0)
Preferred dividends paid by subsidiaries	(0.6)	(1.7)
Payments to redeem cumulative preferred stock	(61.0)	0
Net change in commercial paper	62.3	9.9
Other	(1.6)	(0.9)
Net cash flows from (used for) financing activities	(59.1)	(48.7)
Net increase (decrease) in cash and cash equivalents	1.8	(0.2)
Cash and cash equivalents at beginning of period	0.7	2.7
Cash and cash equivalents at end of period	2.5	2.5
Supplemental cash flows information:
Interest, net of capitalized interest	42.5	40.0
Income taxes, net of refunds	8.5	15.8
Significant non-cash investing and financing activities:
Accrued capital expenditures	$ 36.8	$ 20.8