Condensed Consolidated Statements Of Cash Flows - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Cash flows from operating activities:
Net income	$ 169.3	$ 174.9
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	200.6	191.3
Deferred tax expense and investment tax credits	43.0	37.3
Other	3.5	11.7
Other changes in assets and liabilities:
Accounts receivable	33.7	47.6
Sales of accounts receivable	78.0	(19.0)
Regulatory assets	(22.7)	(71.6)
Derivative assets	3.6	(92.3)
Accounts payable	(25.3)	35.8
Regulatory liabilities	(40.0)	45.2
Deferred income taxes	48.0	51.5
Other	25.6	35.8
Net cash flows from operating activities	517.3	448.2
Cash flows used for investing activities:
Utility construction and acquisition expenditures	(436.2)	(332.6)
Alliant Energy Corporate Services, Inc. and non-regulated businesses construction and acquisition expenditures	(32.2)	(31.9)
Other	(1.9)	(4.5)
Net cash flows used for investing activities	(470.3)	(369.0)
Cash flows used for financing activities:
Common stock dividends	(122.9)	(112.9)
Proceeds from issuance of common stock, net	139.5	0.0
Payments to retire long-term debt	(151.4)	(0.8)
Net change in commercial paper	90.8	28.5
Other	(5.1)	12.4
Net cash flows used for financing activities	(49.1)	(72.8)
Net increase (decrease) in cash and cash equivalents	(2.1)	6.4
Cash and cash equivalents at beginning of period	56.9	9.8
Cash and cash equivalents at end of period	54.8	16.2
Supplemental cash flows information:
Interest, net of capitalized interest	(93.5)	(90.5)
Income taxes, net	0.1	3.8
Significant non-cash investing and financing activities:
Accrued capital expenditures	162.1	124.9
IPL [Member]
Cash flows from operating activities:
Net income	69.6	66.9
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	103.9	97.6
Other	24.9	(4.0)
Other changes in assets and liabilities:
Accounts receivable	16.9	48.3
Sales of accounts receivable	78.0	(19.0)
Gas stored underground	23.6	7.5
Regulatory assets	(20.0)	(48.5)
Derivative assets	(2.7)	(51.9)
Accounts payable	(22.0)	23.4
Regulatory liabilities	(38.9)	(2.7)
Deferred income taxes	44.7	54.7
Other	16.5	33.8
Net cash flows from operating activities	294.5	206.1
Cash flows used for investing activities:
Utility construction and acquisition expenditures	(281.3)	(184.9)
Other	(3.9)	(11.5)
Net cash flows used for investing activities	(285.2)	(196.4)
Cash flows used for financing activities:
Common stock dividends	(69.9)	(70.0)
Capital contributions from parent	100.0	60.0
Payments to retire long-term debt	(150.0)	0.0
Net change in commercial paper	111.2	0.0
Other	(3.9)	1.3
Net cash flows used for financing activities	(12.6)	(8.7)
Net increase (decrease) in cash and cash equivalents	(3.3)	1.0
Cash and cash equivalents at beginning of period	5.3	4.4
Cash and cash equivalents at end of period	2.0	5.4
Supplemental cash flows information:
Interest, net of capitalized interest	(48.3)	(45.2)
Income taxes, net	18.6	9.0
Significant non-cash investing and financing activities:
Accrued capital expenditures	118.8	76.1
WPL [Member]
Cash flows from operating activities:
Net income	84.3	89.4
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	91.8	89.4
Other amortizations	2.7	24.9
Deferred tax expense and investment tax credits	20.4	37.1
Other	(8.1)	(8.1)
Other changes in assets and liabilities:
Regulatory assets	(2.7)	(23.1)
Derivative assets	6.3	(40.4)
Regulatory liabilities	(1.1)	47.9
Other	36.6	18.4
Net cash flows from operating activities	230.2	235.5
Cash flows used for investing activities:
Utility construction and acquisition expenditures	(154.9)	(147.7)
Other	(7.1)	(3.4)
Net cash flows used for investing activities	(162.0)	(151.1)
Cash flows used for financing activities:
Common stock dividends	(63.5)	(59.4)
Net change in commercial paper	0.0	(25.7)
Other	(2.6)	6.6
Net cash flows used for financing activities	(66.1)	(78.5)
Net increase (decrease) in cash and cash equivalents	2.1	5.9
Cash and cash equivalents at beginning of period	46.7	0.5
Cash and cash equivalents at end of period	48.8	6.4
Supplemental cash flows information:
Interest, net of capitalized interest	(46.5)	(42.2)
Income taxes, net	(3.7)	(9.4)
Significant non-cash investing and financing activities:
Accrued capital expenditures	$ 39.5	$ 46.7