Condensed Consolidated Statements Of Cash Flows - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Cash flows from (used for) operating activities:
Net income	$ 102.9	$ 96.8	$ 226.4	$ 199.8
Adjustments to reconcile net income to net cash flows from (used for) operating activities:
Depreciation and amortization			247.4	222.0
Deferred tax expense and tax credits			33.9	49.7
Equity income from unconsolidated investments, net	(10.5)	(11.3)	(31.8)	(22.8)
Other			9.0	12.3
Other changes in assets and liabilities:
Accounts receivable			(507.8)	(304.8)
Regulatory assets			22.6	(66.7)
Accounts payable			(34.1)	(1.0)
Deferred income taxes			(6.3)	60.9
Other			(24.3)	(21.9)
Net cash flows from (used for) operating activities			(65.0)	127.5
Cash flows from (used for) investing activities:
Utility business construction and acquisition expenditures			(699.6)	(565.6)
Other construction and acquisition expenditures			(33.7)	(41.9)
Cash receipts on sold receivables			571.9	374.5
Other			(17.1)	(18.9)
Net cash flows from (used for) investing activities			(178.5)	(251.9)
Cash flows from financing activities:
Common stock dividends			(154.8)	(143.1)
Proceeds from issuance of common stock, net			100.1	137.3
Proceeds from issuance of long-term debt			1,000.0	0.0
Payments to retire long-term debt			(503.0)	(2.4)
Net change in commercial paper and other short-term borrowings			(207.7)	164.5
Other			(13.0)	(32.8)
Net cash flows from financing activities			221.6	123.5
Net increase (decrease) in cash, cash equivalents and restricted cash			(21.9)	(0.9)
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	12.0	12.2	12.0	12.2	33.9
Supplemental cash flows information:
Interest, net of capitalized interest			(119.8)	(105.0)
Income taxes, net			(5.0)	(11.4)
Significant non-cash investing and financing activities:
Accrued capital expenditures			186.5	124.3
Beneficial interest obtained in exchange for securitized accounts receivable			208.3	170.0
IPL [Member]
Cash flows from (used for) operating activities:
Net income	54.2	45.3	103.5	85.1
Adjustments to reconcile net income to net cash flows from (used for) operating activities:
Depreciation and amortization			135.3	114.8
Other			(0.7)	8.7
Other changes in assets and liabilities:
Accounts receivable			(545.6)	(325.3)
Regulatory assets			19.3	(47.5)
Accounts payable			(29.3)	5.0
Regulatory liabilities			19.0	(18.7)
Deferred income taxes			(17.8)	54.2
Other			(10.4)	17.1
Net cash flows from (used for) operating activities			(326.7)	(106.6)
Cash flows from (used for) investing activities:
Utility business construction and acquisition expenditures			(391.1)	(290.2)
Cash receipts on sold receivables			571.9	374.5
Other			(20.4)	(15.7)
Net cash flows from (used for) investing activities			160.4	68.6
Cash flows from financing activities:
Common stock dividends			(84.0)	(78.0)
Capital contributions from parent			130.0	100.0
Net change in commercial paper and other short-term borrowings			125.0	40.0
Other			(6.6)	(23.4)
Net cash flows from financing activities			164.4	38.6
Net increase (decrease) in cash, cash equivalents and restricted cash			(1.9)	0.6
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	5.3	4.8	5.3	4.8	7.2
Supplemental cash flows information:
Interest, net of capitalized interest			(60.2)	(55.7)
Income taxes, net			(0.5)	11.9
Significant non-cash investing and financing activities:
Accrued capital expenditures			93.4	43.2
Beneficial interest obtained in exchange for securitized accounts receivable			208.3	170.0
WPL [Member]
Cash flows from (used for) operating activities:
Net income			93.8	83.6
Adjustments to reconcile net income to net cash flows from (used for) operating activities:
Depreciation and amortization			110.1	105.2
Deferred tax expense and tax credits			14.5	25.2
Other			(8.1)	4.0
Other changes in assets and liabilities:
Accounts receivable			39.0	32.2
Regulatory assets			3.3	(19.2)
Other			(26.7)	(1.1)
Net cash flows from (used for) operating activities			225.9	229.9
Cash flows from (used for) investing activities:
Utility business construction and acquisition expenditures			(308.5)	(307.0)
Other			(17.0)	(15.4)
Net cash flows from (used for) investing activities			(325.5)	(322.4)
Cash flows from financing activities:
Common stock dividends			(70.1)	(63.0)
Capital contributions from parent			150.0	0.0
Net change in commercial paper and other short-term borrowings			1.4	160.2
Other			(1.3)	(6.1)
Net cash flows from financing activities			80.0	91.1
Net increase (decrease) in cash, cash equivalents and restricted cash			(19.6)	(1.4)
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	$ 4.6	$ 5.5	4.6	5.5	$ 24.2
Supplemental cash flows information:
Interest, net of capitalized interest			(49.4)	(45.9)
Income taxes, net			(7.9)	(19.3)
Significant non-cash investing and financing activities:
Accrued capital expenditures			$ 89.6	$ 76.6