Condensed Consolidated Statements Of Cash Flows - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Cash flows from (used for) operating activities:
Net income	$ 123.5	$ 103.0
Adjustments to reconcile net income to net cash flows from (used for) operating activities:
Depreciation and amortization	120.4	107.0
Deferred tax expense and tax credits	17.6	22.7
Other	(14.8)	(7.6)
Other changes in assets and liabilities:
Accounts receivable	(147.6)	(143.2)
Gas stored underground	28.2	25.4
Regulatory assets	(3.4)	(40.6)
Derivative assets	11.0	28.1
Accounts payable	(59.6)	(41.3)
Regulatory liabilities	34.2	14.2
Deferred income taxes	14.9	32.8
Other	(35.1)	18.5
Net cash flows from (used for) operating activities	89.3	119.0
Cash flows from (used for) investing activities:
Utility business construction and acquisition expenditures	(335.2)	(268.9)
Other construction and acquisition expenditures	(20.3)	(22.6)
Cash receipts on sold receivables	284.3	214.7
Other	(14.0)	(10.4)
Net cash flows from (used for) investing activities	(85.2)	(87.2)
Cash flows from (used for) financing activities:
Common stock dividends	(77.5)	(71.5)
Net change in commercial paper	62.1	58.7
Other	5.6	(17.1)
Net cash flows from (used for) financing activities	(9.8)	(29.9)
Net increase (decrease) in cash, cash equivalents and restricted cash	(5.7)	1.9
Cash, cash equivalents and restricted cash at beginning of period	33.9	13.1	$ 13.1
Cash, cash equivalents and restricted cash at end of period	28.2	15.0	33.9
Supplemental cash flows information:
Interest, net of capitalized interest	(54.2)	(51.8)
Income taxes, net	0.0	(2.3)
Significant non-cash investing and financing activities:
Accrued capital expenditures	144.9	139.3
Beneficial interest obtained in exchange for securitized accounts receivable	120.9	149.0
IPL [Member]
Cash flows from (used for) operating activities:
Net income	49.3	39.8
Adjustments to reconcile net income to net cash flows from (used for) operating activities:
Depreciation and amortization	64.8	53.6
Other	0.0	3.1
Other changes in assets and liabilities:
Accounts receivable	(166.7)	(147.0)
Regulatory assets	(3.3)	(29.3)
Accounts payable	(34.3)	(24.7)
Regulatory liabilities	21.7	15.7
Deferred income taxes	11.2	29.1
Other	(7.9)	21.3
Net cash flows from (used for) operating activities	(65.2)	(38.4)
Cash flows from (used for) investing activities:
Utility business construction and acquisition expenditures	(218.2)	(127.6)
Cash receipts on sold receivables	284.3	214.7
Other	(10.5)	(8.7)
Net cash flows from (used for) investing activities	55.6	78.4
Cash flows from (used for) financing activities:
Common stock dividends	(41.9)	(39.1)
Net change in commercial paper	45.9	9.2
Other	4.9	(9.3)
Net cash flows from (used for) financing activities	8.9	(39.2)
Net increase (decrease) in cash, cash equivalents and restricted cash	(0.7)	0.8
Cash, cash equivalents and restricted cash at beginning of period	7.2	4.2	4.2
Cash, cash equivalents and restricted cash at end of period	6.5	5.0	7.2
Supplemental cash flows information:
Interest, net of capitalized interest	(28.2)	(28.4)
Income taxes, net	0.0	(2.6)
Significant non-cash investing and financing activities:
Accrued capital expenditures	68.3	44.2
Beneficial interest obtained in exchange for securitized accounts receivable	120.9	149.0
WPL [Member]
Cash flows from (used for) operating activities:
Net income	54.0	45.5
Adjustments to reconcile net income to net cash flows from (used for) operating activities:
Depreciation and amortization	54.6	52.4
Deferred tax expense and tax credits	6.7	11.8
Other	(4.7)	2.6
Other changes in assets and liabilities:
Accounts receivable	18.7	13.3
Accounts payable	(23.0)	(25.5)
Other	35.4	45.5
Net cash flows from (used for) operating activities	141.7	145.6
Cash flows from (used for) investing activities:
Utility business construction and acquisition expenditures	(117.0)	(141.3)
Other	(11.7)	(8.0)
Net cash flows from (used for) investing activities	(128.7)	(149.3)
Cash flows from (used for) financing activities:
Common stock dividends	(35.0)	(31.5)
Net change in commercial paper	5.6	38.9
Other	(1.9)	(5.8)
Net cash flows from (used for) financing activities	(31.3)	1.6
Net increase (decrease) in cash, cash equivalents and restricted cash	(18.3)	(2.1)
Cash, cash equivalents and restricted cash at beginning of period	24.2	6.9	6.9
Cash, cash equivalents and restricted cash at end of period	5.9	4.8	$ 24.2
Supplemental cash flows information:
Interest, net of capitalized interest	(21.5)	(21.9)
Significant non-cash investing and financing activities:
Accrued capital expenditures	$ 73.9	$ 90.5