Condensed Consolidated Statements Of Cash Flows - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Cash flows from operating activities:
Net income	$ 351.8	$ 330.8
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	299.9	288.4
Deferred tax expense and investment tax credits	101.0	54.2
Other	(2.5)	13.6
Other changes in assets and liabilities:
Accounts receivable	11.7	87.1
Sales of accounts receivable	(21.0)	9.0
Regulatory assets	(51.3)	(154.3)
Regulatory liabilities	(61.5)	61.1
Deferred income taxes	74.1	109.5
Other	(6.9)	(35.5)
Net cash flows from operating activities	695.3	763.9
Cash flows used for investing activities:
Utility construction and acquisition expenditures	(678.9)	(587.4)
Alliant Energy Corporate Services, Inc. and non-regulated businesses construction and acquisition expenditures	(47.5)	(45.1)
Proceeds from Minnesota electric and natural gas distribution asset sales	138.1	0.0
Other	(24.7)	(7.9)
Net cash flows used for investing activities	(613.0)	(640.4)
Cash flows from (used for) financing activities:
Common stock dividends	(185.1)	(169.3)
Proceeds from issuance of common stock, net	145.4	0.0
Proceeds from issuance of long-term debt	250.7	2.9
Payments to retire long-term debt	(182.0)	(47.7)
Net change in commercial paper	(32.2)	74.4
Other	3.2	17.4
Net cash flows from (used for) financing activities	0.0	(122.3)
Net increase (decrease) in cash and cash equivalents	82.3	1.2
Cash and cash equivalents at beginning of period	56.9	9.8
Cash and cash equivalents at end of period	139.2	11.0
Supplemental cash flows information:
Interest, net of capitalized interest	(133.9)	(131.8)
Income taxes, net	0.0	5.3
Significant non-cash investing and financing activities:
Accrued capital expenditures	180.0	141.1
IPL [Member]
Cash flows from operating activities:
Net income	189.6	172.0
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	155.1	146.9
Other	30.9	(12.8)
Other changes in assets and liabilities:
Accounts receivable	(8.3)	57.1
Sales of accounts receivable	(21.0)	9.0
Regulatory assets	(38.1)	(126.1)
Accounts payable	(24.6)	17.9
Regulatory liabilities	(63.1)	14.8
Deferred income taxes	72.0	112.5
Other	25.5	(17.7)
Net cash flows from operating activities	318.0	373.6
Cash flows used for investing activities:
Utility construction and acquisition expenditures	(432.6)	(358.2)
Proceeds from Minnesota electric and natural gas distribution asset sales	138.1	0.0
Other	(24.9)	(18.3)
Net cash flows used for investing activities	(319.4)	(376.5)
Cash flows from (used for) financing activities:
Common stock dividends	(105.0)	(105.0)
Capital contributions from parent	100.0	90.0
Proceeds from issuance of long-term debt	250.0	0.0
Payments to retire long-term debt	(150.0)	(38.4)
Net change in commercial paper	0.0	38.0
Other	0.5	18.5
Net cash flows from (used for) financing activities	95.5	3.1
Net increase (decrease) in cash and cash equivalents	94.1	0.2
Cash and cash equivalents at beginning of period	5.3	4.4
Cash and cash equivalents at end of period	99.4	4.6
Supplemental cash flows information:
Interest, net of capitalized interest	(66.7)	(64.2)
Income taxes, net	31.1	21.0
Significant non-cash investing and financing activities:
Accrued capital expenditures	115.5	96.7
WPL [Member]
Cash flows from operating activities:
Net income	152.2	151.0
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	137.5	135.0
Other amortizations	4.0	36.1
Deferred tax expense and investment tax credits	61.0	58.4
Other	(12.3)	(14.3)
Other changes in assets and liabilities:
Derivative assets	8.8	(32.8)
Regulatory liabilities	1.6	46.3
Derivative liabilities	19.0	(9.7)
Other	4.1	(4.2)
Net cash flows from operating activities	375.9	365.8
Cash flows used for investing activities:
Utility construction and acquisition expenditures	(246.3)	(229.2)
Other	(13.3)	(4.6)
Net cash flows used for investing activities	(259.6)	(233.8)
Cash flows from (used for) financing activities:
Common stock dividends	(95.3)	(89.1)
Payments to retire long-term debt	(30.6)	(8.5)
Net change in commercial paper	0.0	(37.0)
Other	(1.4)	4.4
Net cash flows from (used for) financing activities	(127.3)	(130.2)
Net increase (decrease) in cash and cash equivalents	(11.0)	1.8
Cash and cash equivalents at beginning of period	46.7	0.5
Cash and cash equivalents at end of period	35.7	2.3
Supplemental cash flows information:
Interest, net of capitalized interest	(69.2)	(65.6)
Income taxes, net	(10.0)	(8.7)
Significant non-cash investing and financing activities:
Accrued capital expenditures	$ 57.2	$ 39.9