Consolidated Statements Of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash flows from (used for) operating activities:
Net income	$ 522.3	$ 467.5	$ 381.7
Adjustments to reconcile net income to net cash flows from (used for) operating activities:
Depreciation and amortization	506.9	461.8	411.6
Other amortizations	10.6	21.7	(4.8)
Deferred tax expense and tax credits	67.0	139.6	84.6
Equity (income) loss from unconsolidated investments, net	(54.6)	(44.8)	(39.6)
Distributions from equity method investments	43.9	38.1	28.3
Equity component of allowance for funds used during construction	(51.4)	(33.6)	(42.3)
Asset valuation charges for Franklin County wind farm	0.0	0.0	86.4
Other	7.8	6.7	0.8
Other changes in assets and liabilities:
Accounts receivable	(475.4)	(441.2)	(572.2)
Regulatory assets	(16.2)	(130.8)	(3.6)
Regulatory liabilities	1.3	(83.8)	(63.0)
Deferred income taxes	55.9	81.7	102.4
Other	(90.4)	38.7	22.5
Net cash flows from (used for) operating activities	527.7	521.6	392.8
Cash flows from (used for) investing activities:
Utility construction and acquisition expenditures	(1,568.3)	(1,281.8)	(1,131.2)
Other construction and acquisition expenditures	(65.6)	(185.1)	(65.6)
Cash receipts on sold receivables	605.3	461.8	466.8
Other	(38.2)	(28.3)	9.8
Net cash flows from (used for) investing activities	(1,066.8)	(1,033.4)	(720.2)
Cash flows from (used for) financing activities:
Common stock dividends	(312.2)	(288.3)	(266.5)
Proceeds from issuance of common stock, net	196.6	149.6	26.6
Proceeds from issuance of long-term debt	1,500.0	550.0	800.0
Payments to retire long-term debt	(855.7)	(4.6)	(313.4)
Net change in commercial paper and other short-term borrowings	26.0	171.1	84.3
Other	(24.0)	(45.2)	(1.7)
Net cash flows from (used for) financing activities	530.7	532.6	329.3
Net increase (decrease) in cash, cash equivalents and restricted cash	(8.4)	20.8	1.9
Cash, cash equivalents and restricted cash at beginning of period	33.9	13.1	11.2
Cash, cash equivalents and restricted cash at end of period	25.5	33.9	13.1
Supplemental cash flows information:
Interest, net of capitalized interest	(247.5)	(212.6)	(192.4)
Income taxes, net	(5.0)	(11.3)	(9.8)
Significant non-cash investing and financing activities:
Accrued capital expenditures	299.5	196.5	154.4
Beneficial interest obtained in exchange for securitized accounts receivable	119.4	222.1	211.1
IPL [Member]
Cash flows from (used for) operating activities:
Net income	274.2	227.0	225.8
Adjustments to reconcile net income to net cash flows from (used for) operating activities:
Depreciation and amortization	283.5	245.0	210.8
Deferred tax expense and tax credits	2.2	55.8	35.6
Equity component of allowance for funds used during construction	(28.6)	(21.1)	(35.2)
Other	3.6	1.5	2.9
Other changes in assets and liabilities:
Accounts receivable	(494.0)	(478.7)	(510.5)
Regulatory assets	(20.2)	(126.2)	(54.7)
Accounts payable	(24.9)	24.0	8.0
Regulatory liabilities	0.6	(71.2)	(67.3)
Deferred income taxes	43.8	103.7	97.7
Other	(45.2)	18.4	(18.0)
Net cash flows from (used for) operating activities	(5.0)	(21.8)	(104.9)
Cash flows from (used for) investing activities:
Utility construction and acquisition expenditures	(990.7)	(676.0)	(689.7)
Cash receipts on sold receivables	605.3	461.8	466.8
Other	(44.0)	(27.7)	(5.7)
Net cash flows from (used for) investing activities	(429.4)	(241.9)	(228.6)
Cash flows from (used for) financing activities:
Common stock dividends	(168.0)	(156.1)	(151.9)
Capital contributions from parent	425.0	200.0	190.0
Proceeds from issuance of long-term debt	500.0	250.0	300.0
Payments to retire long-term debt	(350.0)	0.0	0.0
Net change in commercial paper and other short-term borrowings	50.4	0.0	0.0
Other	(17.8)	(27.2)	(7.6)
Net cash flows from (used for) financing activities	439.6	266.7	330.5
Net increase (decrease) in cash, cash equivalents and restricted cash	5.2	3.0	(3.0)
Cash, cash equivalents and restricted cash at beginning of period	7.2	4.2	7.2
Cash, cash equivalents and restricted cash at end of period	12.4	7.2	4.2
Supplemental cash flows information:
Interest, net of capitalized interest	(120.3)	(111.8)	(99.7)
Income taxes, net	(23.8)	8.6	(11.1)
Significant non-cash investing and financing activities:
Accrued capital expenditures	186.6	76.4	53.8
Beneficial interest obtained in exchange for securitized accounts receivable	119.4	222.1	211.1
WPL [Member]
Cash flows from (used for) operating activities:
Net income	208.1	186.6	192.8
Adjustments to reconcile net income to net cash flows from (used for) operating activities:
Depreciation and amortization	219.4	212.9	192.5
Other amortizations	5.8	17.7	(8.7)
Deferred tax expense and tax credits	49.8	53.9	114.5
Equity (income) loss from unconsolidated investments, net	(0.9)	(0.7)	(39.8)
Other	(23.3)	(13.3)	(17.8)
Other changes in assets and liabilities:
Accounts receivable	19.7	17.7	(47.6)
Regulatory assets	4.0	(4.7)	51.1
Other	(26.5)	(5.1)	44.6
Net cash flows from (used for) operating activities	457.0	465.7	521.4
Cash flows from (used for) investing activities:
Utility construction and acquisition expenditures	(577.6)	(637.4)	(453.0)
Other	(29.9)	(29.9)	(25.9)
Net cash flows from (used for) investing activities	(607.5)	(667.3)	(478.9)
Cash flows from (used for) financing activities:
Common stock dividends	(140.1)	(125.9)	(135.0)
Capital contributions from parent	200.0	90.0	60.0
Proceeds from issuance of long-term debt	0.0	300.0	0.0
Net change in commercial paper and other short-term borrowings	80.5	(27.3)	32.4
Other	(4.9)	(17.9)	3.9
Net cash flows from (used for) financing activities	135.5	218.9	(38.7)
Net increase (decrease) in cash, cash equivalents and restricted cash	(15.0)	17.3	3.8
Cash, cash equivalents and restricted cash at beginning of period	24.2	6.9	3.1
Cash, cash equivalents and restricted cash at end of period	9.2	24.2	6.9
Supplemental cash flows information:
Interest, net of capitalized interest	(98.1)	(91.7)	(91.5)
Income taxes, net	14.0	(8.4)	27.8
Significant non-cash investing and financing activities:
Accrued capital expenditures	102.5	114.5	93.1
Transfer of investment in ATC and tax liability to ATI	$ 0.0	$ 0.0	$ (163.6)