Condensed Consolidated Statements Of Cash Flows - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Cash flows from operating activities:
Net income	$ 371.2	$ 316.5
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	342.7	308.7
Deferred tax expense and tax credits	102.7	76.7
Asset valuation charges for Franklin County wind farm	0.0	86.4
Other	(7.1)	(44.0)
Other changes in assets and liabilities:
Accounts receivable	72.8	(101.0)
Sales of accounts receivable	91.0	(4.0)
Regulatory assets	(108.9)	36.6
Regulatory liabilities	(64.8)	(66.5)
Deferred income taxes	101.0	71.8
Other	(17.2)	(27.2)
Net cash flows from operating activities	883.4	654.0
Cash flows used for investing activities:
Utility business construction and acquisition expenditures	(909.7)	(743.6)
Alliant Energy Corporate Services, Inc. and non-regulated businesses construction and acquisition expenditures	(139.7)	(43.3)
Other	(22.9)	15.1
Net cash flows used for investing activities	(1,072.3)	(771.8)
Cash flows from (used for) financing activities:
Common stock dividends	(215.7)	(199.8)
Proceeds from issuance of common stock, net	143.2	20.4
Proceeds from issuance of long-term debt	0.0	300.0
Net change in commercial paper and other short-term borrowings	281.2	78.5
Other	(18.8)	(2.4)
Net cash flows from (used for) financing activities	189.9	196.7
Net increase (decrease) in cash and cash equivalents	1.0	78.9
Cash and cash equivalents at beginning of period	8.2	5.8
Cash and cash equivalents at end of period	9.2	84.7
Supplemental cash flows information:
Interest, net of capitalized interest	(158.5)	(140.7)
Income taxes, net	(11.4)	(8.3)
Significant non-cash investing and financing activities:
Accrued capital expenditures	197.2	99.9
IPL [Member]
Cash flows from operating activities:
Net income	208.1	199.3
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	181.0	157.8
Other	26.2	24.3
Other changes in assets and liabilities:
Accounts receivable	12.4	(66.5)
Sales of accounts receivable	91.0	(4.0)
Regulatory assets	(107.8)	(14.1)
Regulatory liabilities	(49.6)	(64.5)
Deferred income taxes	88.9	67.7
Other	20.4	(43.5)
Net cash flows from operating activities	470.6	256.5
Cash flows used for investing activities:
Utility business construction and acquisition expenditures	(470.1)	(436.5)
Other	(23.5)	1.1
Net cash flows used for investing activities	(493.6)	(435.4)
Cash flows from (used for) financing activities:
Common stock dividends	(117.0)	(114.0)
Capital contributions from parent	100.0	65.0
Proceeds from issuance of long-term debt	0.0	300.0
Net change in commercial paper and other short-term borrowings	44.0	0.0
Other	(2.6)	1.1
Net cash flows from (used for) financing activities	24.4	252.1
Net increase (decrease) in cash and cash equivalents	1.4	73.2
Cash and cash equivalents at beginning of period	3.3	4.5
Cash and cash equivalents at end of period	4.7	77.7
Supplemental cash flows information:
Interest, net of capitalized interest	(84.1)	(72.5)
Income taxes, net	13.2	0.7
Significant non-cash investing and financing activities:
Accrued capital expenditures	71.0	44.5
WPL [Member]
Cash flows from operating activities:
Net income	133.4	160.3
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	158.8	143.5
Deferred tax expense and tax credits	60.1	97.9
Other	4.8	(20.3)
Other changes in assets and liabilities:
Accounts receivable	41.8	(12.8)
Regulatory assets	(1.1)	50.7
Other	(36.6)	20.0
Net cash flows from operating activities	361.2	439.3
Cash flows used for investing activities:
Utility business construction and acquisition expenditures	(454.0)	(307.1)
Other	(16.2)	(19.6)
Net cash flows used for investing activities	(470.2)	(326.7)
Cash flows from (used for) financing activities:
Common stock dividends	(94.5)	(101.2)
Capital contributions from parent	40.0	0.0
Net change in commercial paper and other short-term borrowings	172.3	(8.1)
Other	(9.8)	1.9
Net cash flows from (used for) financing activities	108.0	(107.4)
Net increase (decrease) in cash and cash equivalents	(1.0)	5.2
Cash and cash equivalents at beginning of period	4.2	0.4
Cash and cash equivalents at end of period	3.2	5.6
Supplemental cash flows information:
Interest, net of capitalized interest	(68.1)	(67.7)
Income taxes, net	(20.2)	19.6
Significant non-cash investing and financing activities:
Accrued capital expenditures	$ 122.3	$ 50.8