Condensed Consolidated Statements Of Cash Flows - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Cash flows from operating activities:
Net income	$ 316.5	$ 351.8
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	308.7	299.9
Deferred tax expense and investment tax credits	76.7	101.0
Asset valuation charges for Franklin County wind farm	86.4	0.0
Other	(44.0)	(2.5)
Other changes in assets and liabilities:
Accounts receivable	(101.0)	11.7
Sales of accounts receivable	(4.0)	(21.0)
Regulatory assets	36.6	(51.3)
Regulatory liabilities	(66.5)	(61.5)
Deferred income taxes	71.8	74.1
Other	(27.2)	(6.9)
Net cash flows from operating activities	654.0	695.3
Cash flows used for investing activities:
Utility business construction and acquisition expenditures	(743.6)	(678.9)
Alliant Energy Corporate Services, Inc. and non-regulated businesses construction and acquisition expenditures	(43.3)	(47.5)
Proceeds from Minnesota electric and natural gas distribution asset sales	0.0	138.1
Other	15.1	(24.7)
Net cash flows used for investing activities	(771.8)	(613.0)
Cash flows from (used for) financing activities:
Common stock dividends	(199.8)	(185.1)
Proceeds from issuance of common stock, net	20.4	145.4
Proceeds from issuance of long-term debt	300.0	250.7
Payments to retire long-term debt	(1.9)	(182.0)
Net change in commercial paper	78.5	(32.2)
Other	(0.5)	3.2
Net cash flows from (used for) financing activities	196.7	0.0
Net increase (decrease) in cash and cash equivalents	78.9	82.3
Cash and cash equivalents at beginning of period	5.8	56.9
Cash and cash equivalents at end of period	84.7	139.2
Supplemental cash flows information:
Interest, net of capitalized interest	(140.7)	(133.9)
Income taxes, net	(8.3)	0.0
Significant non-cash investing and financing activities:
Accrued capital expenditures	99.9	180.0
IPL [Member]
Cash flows from operating activities:
Net income	199.3	188.2
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	157.8	155.1
Other	24.3	32.3
Other changes in assets and liabilities:
Accounts receivable	(66.5)	(8.3)
Sales of accounts receivable	(4.0)	(21.0)
Regulatory assets	(14.1)	(38.1)
Regulatory liabilities	(64.5)	(63.1)
Deferred income taxes	67.7	72.0
Other	(43.5)	0.9
Net cash flows from operating activities	256.5	318.0
Cash flows used for investing activities:
Utility business construction and acquisition expenditures	(436.5)	(432.6)
Proceeds from Minnesota electric and natural gas distribution asset sales	0.0	138.1
Other	1.1	(24.9)
Net cash flows used for investing activities	(435.4)	(319.4)
Cash flows from (used for) financing activities:
Common stock dividends	(114.0)	(105.0)
Capital contributions from parent	65.0	100.0
Proceeds from issuance of long-term debt	300.0	250.0
Payments to retire long-term debt	0.0	(150.0)
Other	1.1	0.5
Net cash flows from (used for) financing activities	252.1	95.5
Net increase (decrease) in cash and cash equivalents	73.2	94.1
Cash and cash equivalents at beginning of period	4.5	5.3
Cash and cash equivalents at end of period	77.7	99.4
Supplemental cash flows information:
Interest, net of capitalized interest	(72.5)	(66.7)
Income taxes, net	0.7	31.1
Significant non-cash investing and financing activities:
Accrued capital expenditures	44.5	115.5
WPL [Member]
Cash flows from operating activities:
Net income	160.3	153.2
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	143.5	137.5
Deferred tax expense and investment tax credits	97.9	60.0
Other	(20.3)	(8.3)
Other changes in assets and liabilities:
Regulatory assets	50.7	(13.2)
Derivative liabilities	(13.3)	19.0
Other	20.5	27.7
Net cash flows from operating activities	439.3	375.9
Cash flows used for investing activities:
Utility business construction and acquisition expenditures	(307.1)	(246.3)
Other	(19.6)	(13.3)
Net cash flows used for investing activities	(326.7)	(259.6)
Cash flows from (used for) financing activities:
Common stock dividends	(101.2)	(95.3)
Payments to retire long-term debt	0.0	(30.6)
Other	(6.2)	(1.4)
Net cash flows from (used for) financing activities	(107.4)	(127.3)
Net increase (decrease) in cash and cash equivalents	5.2	(11.0)
Cash and cash equivalents at beginning of period	0.4	46.7
Cash and cash equivalents at end of period	5.6	35.7
Supplemental cash flows information:
Interest, net of capitalized interest	(67.7)	(69.2)
Income taxes, net	19.6	(10.0)
Significant non-cash investing and financing activities:
Accrued capital expenditures	$ 50.8	$ 57.2