Consolidated Statements Of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flows from (used for) operating activities:
Net income	$ 567.4	$ 522.3	$ 467.5
Adjustments to reconcile net income to net cash flows from (used for) operating activities:
Depreciation and amortization	567.2	506.9	461.8
Deferred tax expense and tax credits	55.6	67.0	139.6
Equity component of allowance for funds used during construction	(65.5)	(51.4)	(33.6)
Other	19.9	7.7	21.7
Other changes in assets and liabilities:
Accounts receivable	(471.7)	(475.4)	(441.2)
Regulatory assets	(16.2)	(16.2)	(130.8)
Regulatory liabilities	(40.3)	1.3	(83.8)
Deferred income taxes	53.8	55.9	81.7
Other	(9.8)	(90.4)	38.7
Net cash flows from (used for) operating activities	660.4	527.7	521.6
Cash flows used for investing activities:
Utility construction and acquisition expenditures	(1,538.4)	(1,568.3)	(1,281.8)
Other construction and acquisition expenditures	(101.7)	(65.6)	(185.1)
Cash receipts on sold receivables	413.2	605.3	461.8
Other	(60.4)	(38.2)	(28.3)
Net cash flows used for investing activities	(1,287.3)	(1,066.8)	(1,033.4)
Cash flows from financing activities:
Common stock dividends	(337.7)	(312.2)	(288.3)
Proceeds from issuance of common stock, net	390.3	196.6	149.6
Proceeds from issuance of long-term debt	950.0	1,500.0	550.0
Payments to retire long-term debt	(256.5)	(855.7)	(4.6)
Net change in commercial paper and other short-term borrowings	(103.8)	26.0	171.1
Other	(23.2)	(24.0)	(45.2)
Net cash flows from (used for) financing activities	619.1	530.7	532.6
Net increase (decrease) in cash, cash equivalents and restricted cash	(7.8)	(8.4)	20.8
Cash, cash equivalents and restricted cash at beginning of period	25.5	33.9	13.1
Cash, cash equivalents and restricted cash at end of period	17.7	25.5	33.9
Supplemental cash flows information:
Interest	(267.9)	(247.5)	(212.6)
Income taxes, net	20.5	(5.0)	(11.3)
Significant non-cash investing and financing activities:
Accrued capital expenditures	195.8	299.5	196.5
Beneficial interest obtained in exchange for securitized accounts receivable	187.7	119.4	222.1
IPL [Member]
Cash flows from (used for) operating activities:
Net income	294.3	274.2	227.0
Adjustments to reconcile net income to net cash flows from (used for) operating activities:
Depreciation and amortization	326.7	283.5	245.0
Deferred tax expense and tax credits	15.3	2.2	55.8
Equity component of allowance for funds used during construction	(35.2)	(28.6)	(21.1)
Other	1.0	3.6	1.5
Other changes in assets and liabilities:
Accounts receivable	(466.6)	(494.0)	(478.7)
Regulatory assets	(11.5)	(20.2)	(126.2)
Accounts payable	(20.5)	(24.9)	24.0
Regulatory liabilities	2.0	0.6	(71.2)
Deferred income taxes	35.2	43.8	103.7
Other	32.2	(45.2)	18.4
Net cash flows from (used for) operating activities	172.9	(5.0)	(21.8)
Cash flows used for investing activities:
Utility construction and acquisition expenditures	(1,019.6)	(990.7)	(676.0)
Cash receipts on sold receivables	413.2	605.3	461.8
Other	(60.6)	(44.0)	(27.7)
Net cash flows used for investing activities	(667.0)	(429.4)	(241.9)
Cash flows from financing activities:
Common stock dividends	(168.0)	(168.0)	(156.1)
Capital contributions from parent	125.0	425.0	200.0
Proceeds from issuance of long-term debt	600.0	500.0	250.0
Payments to retire long-term debt	0.0	(350.0)	0.0
Net change in commercial paper and other short-term borrowings	(50.4)	50.4	0.0
Other	(15.6)	(17.8)	(27.2)
Net cash flows from (used for) financing activities	491.0	439.6	266.7
Net increase (decrease) in cash, cash equivalents and restricted cash	(3.1)	5.2	3.0
Cash, cash equivalents and restricted cash at beginning of period	12.4	7.2	4.2
Cash, cash equivalents and restricted cash at end of period	9.3	12.4	7.2
Supplemental cash flows information:
Interest	(121.6)	(120.3)	(111.8)
Income taxes, net	6.9	(23.8)	8.6
Significant non-cash investing and financing activities:
Accrued capital expenditures	111.6	186.6	76.4
Beneficial interest obtained in exchange for securitized accounts receivable	187.7	119.4	222.1
WPL [Member]
Cash flows from (used for) operating activities:
Net income	233.0	208.1	186.6
Adjustments to reconcile net income to net cash flows from (used for) operating activities:
Depreciation and amortization	235.6	219.4	212.9
Deferred tax expense and tax credits	23.6	49.8	53.9
Other	(11.5)	(17.5)	4.4
Other changes in assets and liabilities:
Regulatory liabilities	(42.3)	0.7	(12.6)
Other	(15.2)	(3.5)	20.5
Net cash flows from (used for) operating activities	423.2	457.0	465.7
Cash flows used for investing activities:
Utility construction and acquisition expenditures	(518.8)	(577.6)	(637.4)
Other	(38.4)	(29.9)	(29.9)
Net cash flows used for investing activities	(557.2)	(607.5)	(667.3)
Cash flows from financing activities:
Common stock dividends	(143.9)	(140.1)	(125.9)
Capital contributions from parent	125.0	200.0	90.0
Proceeds from issuance of long-term debt	350.0	0.0	300.0
Payments to retire long-term debt	(250.0)	0.0	0.0
Net change in commercial paper and other short-term borrowings	62.7	80.5	(27.3)
Other	(14.6)	(4.9)	(17.9)
Net cash flows from (used for) financing activities	129.2	135.5	218.9
Net increase (decrease) in cash, cash equivalents and restricted cash	(4.8)	(15.0)	17.3
Cash, cash equivalents and restricted cash at beginning of period	9.2	24.2	6.9
Cash, cash equivalents and restricted cash at end of period	4.4	9.2	24.2
Supplemental cash flows information:
Interest	(102.5)	(98.1)	(91.7)
Income taxes, net	(28.9)	14.0	(8.4)
Significant non-cash investing and financing activities:
Accrued capital expenditures	$ 81.5	$ 102.5	$ 114.5