Condensed Consolidated Statements Of Cash Flows (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012
Cash flows from operating activities:
Net income	$ 308.1	$ 263.4
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	277.4	247.9
Other amortizations	29.1	41.3
Deferred taxes and investment tax credits	92.2	85.6
Equity income from unconsolidated investments, net	(32.7)	(30.4)
Distributions from equity method investments	26.6	25.7
Other	(14.1)	(8.4)
Other changes in assets and liabilities:
Accounts receivable	(12.8)	50.9
Sales of accounts receivable	10.0	(85.0)
Regulatory assets	(14.4)	(73.5)
Regulatory liabilities	(74.9)	5.0
Deferred income taxes	75.4	90.5
Other	(26.8)	(12.7)
Net cash flows from operating activities	643.1	600.3
Cash flows used for investing activities:
Utility construction and acquisition expenditures	(524.4)	(412.7)
Alliant Energy Corporate Services, Inc. and non-regulated businesses construction and acquisition expenditures	(35.9)	(106.3)
Proceeds from Franklin County wind project cash grant	62.4	0
Other	(15.3)	1.3
Net cash flows used for investing activities	(513.2)	(517.7)
Cash flows from (used for) financing activities:
Common stock dividends	(156.2)	(149.6)
Preferred dividends paid by subsidiaries	(8.9)	(11.9)
Payments to redeem cumulative preferred stock	(211.0)	0
Proceeds from issuance of cumulative preferred stock	200.0	0
Proceeds from issuance of long-term debt	0	75.0
Net change in commercial paper	34.8	17.6
Other	7.9	16.0
Net cash flows from (used for) financing activities	(133.4)	(52.9)
Net increase (decrease) in cash and cash equivalents	(3.5)	29.7
Cash and cash equivalents at beginning of period	21.2	11.4
Cash and cash equivalents at end of period	17.7	41.1
Supplemental cash flows information:
Interest, net of capitalized interest	128.5	115.6
Income taxes, net of refunds	(9.7)	(0.8)
Significant non-cash investing and financing activities:
Accrued capital expenditures	100.5	123.8
IPL [Member]
Cash flows from operating activities:
Net income	168.8	124.6
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	142.8	141.1
Other	1.2	(3.8)
Other changes in assets and liabilities:
Accounts receivable	(53.0)	(2.6)
Sales of accounts receivable	10.0	(85.0)
Regulatory assets	(9.8)	(57.7)
Regulatory liabilities	(68.3)	(27.5)
Deferred income taxes	71.0	88.9
Other	(3.0)	(5.6)
Net cash flows from operating activities	259.7	172.4
Cash flows used for investing activities:
Utility construction and acquisition expenditures	(274.3)	(194.6)
Other	(15.5)	(16.5)
Net cash flows used for investing activities	(289.8)	(211.1)
Cash flows from (used for) financing activities:
Common stock dividends	(95.7)	(91.6)
Preferred dividends paid by subsidiaries	(8.3)	(9.4)
Capital contributions from parent	90.0	80.0
Payments to redeem cumulative preferred stock	(150.0)	0
Proceeds from issuance of cumulative preferred stock	200.0	0
Net change in commercial paper	(11.3)	42.9
Other	7.2	20.0
Net cash flows from (used for) financing activities	31.9	41.9
Net increase (decrease) in cash and cash equivalents	1.8	3.2
Cash and cash equivalents at beginning of period	4.5	2.1
Cash and cash equivalents at end of period	6.3	5.3
Supplemental cash flows information:
Interest, net of capitalized interest	60.9	58.5
Income taxes, net of refunds	10.7	(11.3)
Significant non-cash investing and financing activities:
Accrued capital expenditures	57.4	69.2
WPL [Member]
Cash flows from operating activities:
Net income	139.3	124.7
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	129.0	104.8
Other amortizations	21.9	32.7
Deferred taxes and investment tax credits	71.6	89.3
Equity income from unconsolidated investments, net	(32.7)	(31.2)
Distributions from equity method investments	26.6	25.7
Other	(5.4)	(8.9)
Other changes in assets and liabilities:
Accounts receivable	28.0	9.9
Income tax refunds receivable	3.5	(22.3)
Regulatory assets	(4.6)	(15.8)
Regulatory liabilities	(6.6)	32.5
Accrued taxes	(17.1)	0.3
Other	2.7	(2.1)
Net cash flows from operating activities	356.2	339.6
Cash flows used for investing activities:
Utility construction and acquisition expenditures	(250.1)	(218.1)
Other	(2.3)	5.6
Net cash flows used for investing activities	(252.4)	(212.5)
Cash flows from (used for) financing activities:
Common stock dividends	(87.2)	(84.1)
Preferred dividends paid by subsidiaries	(0.6)	(2.5)
Payments to redeem cumulative preferred stock	(61.0)	0
Net change in commercial paper	56.8	(25.7)
Other	(5.9)	(1.3)
Net cash flows from (used for) financing activities	(97.9)	(113.6)
Net increase (decrease) in cash and cash equivalents	5.9	13.5
Cash and cash equivalents at beginning of period	0.7	2.7
Cash and cash equivalents at end of period	6.6	16.2
Supplemental cash flows information:
Interest, net of capitalized interest	65.9	63.1
Income taxes, net of refunds	(0.6)	7.9
Significant non-cash investing and financing activities:
Accrued capital expenditures	$ 39.2	$ 45.0