Condensed Consolidated Statements Of Cash Flows - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Cash flows from operating activities:
Net income	$ 127.7	$ 123.5
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	136.9	120.4
Deferred tax expense and tax credits	21.7	17.6
Other	(10.1)	(14.8)
Other changes in assets and liabilities:
Accounts receivable	(121.6)	(80.6)
Gas stored underground	33.1	28.2
Accounts payable	(42.7)	(59.6)
Regulatory liabilities	14.1	34.2
Other	22.0	(12.6)
Net cash flows from operating activities	181.1	156.3
Cash flows used for investing activities:
Utility business construction and acquisition expenditures	(374.0)	(335.2)
Other construction and acquisition expenditures	(32.1)	(20.3)
Cash receipts on sold receivables	53.4	217.3
Other	(12.1)	(14.0)
Net cash flows used for investing activities	(364.8)	(152.2)
Cash flows from (used for) financing activities:
Common stock dividends	(83.7)	(77.5)
Proceeds from issuance of common stock, net	54.6	6.3
Net change in commercial paper	188.5	62.1
Other	16.6	(0.7)
Net cash flows from (used for) financing activities	176.0	(9.8)
Net decrease in cash, cash equivalents and restricted cash	(7.7)	(5.7)
Cash, cash equivalents and restricted cash at beginning of period	25.5	33.9
Cash, cash equivalents and restricted cash at end of period	17.8	28.2
Supplemental cash flows information:
Interest, net of capitalized interest	(62.9)	(54.2)
Income taxes, net	6.8	0.0
Significant non-cash investing and financing activities:
Accrued capital expenditures	167.5	144.9
Beneficial interest obtained in exchange for securitized accounts receivable	178.3	120.9
IPL [Member]
Cash flows from operating activities:
Net income	55.9	49.3
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	77.1	64.8
Other	(10.1)	0.0
Other changes in assets and liabilities:
Accounts receivable	(112.6)	(99.7)
Gas stored underground	20.7	16.7
Accounts payable	(15.0)	(34.3)
Regulatory liabilities	17.4	21.7
Other	43.3	(16.7)
Net cash flows from operating activities	76.7	1.8
Cash flows used for investing activities:
Utility business construction and acquisition expenditures	(261.3)	(218.2)
Cash receipts on sold receivables	53.4	217.3
Other	(13.9)	(10.5)
Net cash flows used for investing activities	(221.8)	(11.4)
Cash flows from (used for) financing activities:
Common stock dividends	(42.0)	(41.9)
Capital contributions from parent	100.0	0.0
Net change in commercial paper	64.6	45.9
Other	17.0	4.9
Net cash flows from (used for) financing activities	139.6	8.9
Net decrease in cash, cash equivalents and restricted cash	(5.5)	(0.7)
Cash, cash equivalents and restricted cash at beginning of period	12.4	7.2
Cash, cash equivalents and restricted cash at end of period	6.9	6.5
Supplemental cash flows information:
Interest, net of capitalized interest	(36.0)	(28.2)
Income taxes, net	6.8	0.0
Significant non-cash investing and financing activities:
Accrued capital expenditures	106.6	68.3
Beneficial interest obtained in exchange for securitized accounts receivable	178.3	120.9
WPL [Member]
Cash flows from operating activities:
Net income	65.7	54.0
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	58.6	54.6
Deferred tax expense and tax credits	14.8	6.7
Other	(2.0)	(4.7)
Other changes in assets and liabilities:
Accounts receivable	(10.3)	18.7
Accounts payable	(28.7)	(23.0)
Other	24.1	35.4
Net cash flows from operating activities	122.2	141.7
Cash flows used for investing activities:
Utility business construction and acquisition expenditures	(112.7)	(117.0)
Other	(7.6)	(11.7)
Net cash flows used for investing activities	(120.3)	(128.7)
Cash flows from (used for) financing activities:
Common stock dividends	(36.0)	(35.0)
Net change in commercial paper	32.9	5.6
Other	(3.3)	(1.9)
Net cash flows from (used for) financing activities	(6.4)	(31.3)
Net decrease in cash, cash equivalents and restricted cash	(4.5)	(18.3)
Cash, cash equivalents and restricted cash at beginning of period	9.2	24.2
Cash, cash equivalents and restricted cash at end of period	4.7	5.9
Supplemental cash flows information:
Interest, net of capitalized interest	(22.5)	(21.5)
Significant non-cash investing and financing activities:
Accrued capital expenditures	$ 57.3	$ 73.9