Condensed Consolidated Statements Of Cash Flows - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Cash flows from operating activities:
Net income	$ 99.1	$ 99.2
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	102.5	100.2
Deferred tax expense and investment tax credits	22.8	29.7
Other	(17.6)	(0.1)
Other changes in assets and liabilities:
Accounts receivable	(47.8)	6.6
Sales of accounts receivable	57.0	52.0
Gas stored underground	27.4	49.5
Accounts payable	(31.2)	(32.8)
Regulatory liabilities	(28.7)	(6.6)
Other	44.8	17.0
Net cash flows from operating activities	228.3	314.7
Cash flows used for investing activities:
Utility construction and acquisition expenditures	(220.4)	(226.0)
Alliant Energy Corporate Services, Inc. and non-regulated businesses construction and acquisition expenditures	(18.8)	(19.8)
Other	19.2	(5.1)
Net cash flows used for investing activities	(220.0)	(250.9)
Cash flows from (used for) financing activities:
Common stock dividends	(66.5)	(60.7)
Proceeds from issuance of common stock, net	6.2	122.1
Net change in commercial paper	53.6	(99.8)
Other	(2.6)	15.3
Net cash flows from (used for) financing activities	(9.3)	(23.1)
Net increase (decrease) in cash and cash equivalents	(1.0)	40.7
Cash and cash equivalents at beginning of period	5.8	56.9
Cash and cash equivalents at end of period	4.8	97.6
Supplemental cash flows information:
Interest, net of capitalized interest	(44.5)	(40.2)
Income taxes, net	0.0	0.1
Significant non-cash investing and financing activities:
Accrued capital expenditures	105.0	119.0
IPL [Member]
Cash flows from operating activities:
Net income	48.2	50.1
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	52.7	51.8
Other	3.2	12.8
Other changes in assets and liabilities:
Accounts receivable	(37.5)	(2.2)
Sales of accounts receivable	57.0	52.0
Gas stored underground	15.1	26.4
Accounts payable	(19.5)	(36.1)
Regulatory liabilities	(23.6)	(11.8)
Other	20.8	27.1
Net cash flows from operating activities	116.4	170.1
Cash flows used for investing activities:
Utility construction and acquisition expenditures	(135.3)	(150.6)
Other	12.1	(5.7)
Net cash flows used for investing activities	(123.2)	(156.3)
Cash flows from (used for) financing activities:
Common stock dividends	(38.1)	(35.0)
Capital contributions from parent	40.0	0.0
Other	3.4	18.5
Net cash flows from (used for) financing activities	5.3	(16.5)
Net increase (decrease) in cash and cash equivalents	(1.5)	(2.7)
Cash and cash equivalents at beginning of period	4.5	5.3
Cash and cash equivalents at end of period	3.0	2.6
Supplemental cash flows information:
Interest, net of capitalized interest	(22.6)	(18.4)
Income taxes, net	1.1	6.2
Significant non-cash investing and financing activities:
Accrued capital expenditures	47.6	82.8
WPL [Member]
Cash flows from operating activities:
Net income	47.0	45.1
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	47.4	46.0
Deferred tax expense and investment tax credits	18.8	10.1
Other	(10.9)	(0.9)
Other changes in assets and liabilities:
Gas stored underground	12.3	23.1
Accounts payable	(15.3)	4.0
Derivative liabilities	19.5	4.6
Other	4.8	25.8
Net cash flows from operating activities	123.6	157.8
Cash flows used for investing activities:
Utility construction and acquisition expenditures	(85.1)	(75.4)
Other	(6.3)	(3.0)
Net cash flows used for investing activities	(91.4)	(78.4)
Cash flows from (used for) financing activities:
Common stock dividends	(33.8)	(31.8)
Other	2.5	(3.4)
Net cash flows from (used for) financing activities	(31.3)	(35.2)
Net increase (decrease) in cash and cash equivalents	0.9	44.2
Cash and cash equivalents at beginning of period	0.4	46.7
Cash and cash equivalents at end of period	1.3	90.9
Supplemental cash flows information:
Interest, net of capitalized interest	(21.9)	(22.6)
Income taxes, net	(7.4)	9.1
Significant non-cash investing and financing activities:
Accrued capital expenditures	$ 49.7	$ 32.9