v2.4.0.6
Condensed Consolidated Statements Of Cash Flows (USD $)
In Millions, unless otherwise specified
 9 Months Ended
Sep. 30, 2012
Sep. 30, 2011
Cash flows from operating activities:    
Net income $ 263.4 $ 260.9
Adjustments to reconcile net income (loss) to net cash flows from operating activities:    
Depreciation and amortization 247.9 242.3
Other amortizations 41.3 42.1
Deferred tax expense (benefit) and investment tax credits 85.6 30.7
Equity income from unconsolidated investments, net (30.4) (29.6)
Distributions from equity method investments 25.7 24.4
Other (8.4) 13.5
Other changes in assets and liabilities:    
Accounts receivable 50.9 (49.7)
Sales of accounts receivable (85.0) 50.0
Production fuel (8.6) 27.7
Regulatory assets (73.5) (191.1)
Accounts payable 47.2 25.9
Regulatory liabilities 5.0 158.5
Pension and other benefit obligations (1.9) (67.9)
Other (49.4) (21.8)
Net cash flows from operating activities 600.3 612.7
Cash flows used for investing activities:    
Utility construction and acquisition expenditures (412.7) (480.2)
Alliant Energy Corporate Services, Inc. and non-regulated businesses (106.3) (46.1)
Other 1.3 19.9
Net cash flows used for investing activities (517.7) (506.4)
Cash flows from (used for) financing activities:    
Common stock dividends (149.6) (141.1)
Preferred dividends paid by subsidiaries (11.9) (12.9)
Payments to redeem cumulative preferred stock of IPL 0 (40.0)
Proceeds from issuance of long-term debt 75.0 0.4
Net change in commercial paper 17.6 (25.3)
Other 16.0 (1.0)
Net cash flows from (used for) financing activities (52.9) (219.9)
Net increase (decrease) in cash and cash equivalents 29.7 (113.6)
Cash and cash equivalents at beginning of period 11.4 159.3
Cash and cash equivalents at end of period 41.1 45.7
Supplemental cash flows information:    
Interest, net of capitalized interest 115.6 119.0
Income taxes, net of refunds (0.8) (3.0)
Significant noncash investing and financing activities:    
Accrued capital expenditures 123.8 27.7
IPL [Member]
    
Cash flows from operating activities:    
Net income 124.6 129.5
Adjustments to reconcile net income (loss) to net cash flows from operating activities:    
Depreciation and amortization 141.1 134.1
Deferred tax expense (benefit) and investment tax credits (9.2) (31.1)
Other 5.4 17.6
Other changes in assets and liabilities:    
Accounts receivable (2.6) 14.3
Sales of accounts receivable (85.0) 50.0
Production fuel (8.4) 19.3
Regulatory assets (57.7) (202.0)
Accounts payable 27.4 (2.3)
Accrued taxes (5.8) (28.2)
Regulatory liabilities (27.5) 145.1
Pension and other benefit obligations (2.1) (37.5)
Other (16.7) 10.7
Net cash flows from operating activities 172.4 314.1
Cash flows used for investing activities:    
Utility construction and acquisition expenditures (194.6) (232.3)
Proceeds from sale of wind project assets to affiliate 0 115.3
Other (16.5) (15.2)
Net cash flows used for investing activities (211.1) (132.2)
Cash flows from (used for) financing activities:    
Common stock dividends (91.6) (43.7)
Preferred dividends paid by subsidiaries (9.4) (10.4)
Capital contributions from parent 80.0 0
Repayment of capital to parent 0 (100.7)
Payments to redeem cumulative preferred stock of IPL 0 (40.0)
Net change in commercial paper 42.9 0
Changes in cash overdrafts 20.0 7.3
Other 0 0.1
Net cash flows from (used for) financing activities 41.9 (187.4)
Net increase (decrease) in cash and cash equivalents 3.2 (5.5)
Cash and cash equivalents at beginning of period 2.1 5.7
Cash and cash equivalents at end of period 5.3 0.2
Supplemental cash flows information:    
Interest, net of capitalized interest 58.5 58.3
Income taxes, net of refunds (11.3) 15.0
Significant noncash investing and financing activities:    
Accrued capital expenditures 69.2 11.3
WPL [Member]
    
Cash flows from operating activities:    
Net income 124.7 120.8
Adjustments to reconcile net income (loss) to net cash flows from operating activities:    
Depreciation and amortization 104.8 104.5
Other amortizations 32.7 31.8
Deferred tax expense (benefit) and investment tax credits 89.3 77.3
Equity income from unconsolidated investments, net (31.2) (28.9)
Distributions from equity method investments 25.7 24.4
Other (8.9) 6.9
Other changes in assets and liabilities:    
Accounts receivable 9.9 27.5
Income tax refunds receivable (22.3) 25.1
Regulatory assets (15.8) 10.9
Regulatory liabilities 32.5 13.4
Pension and other benefit obligations (0.2) (15.5)
Other (3.9) (21.8)
Net cash flows from operating activities 339.6 381.3
Cash flows used for investing activities:    
Utility construction and acquisition expenditures (218.1) (247.9)
Other 5.6 5.5
Net cash flows used for investing activities (212.5) (242.4)
Cash flows from (used for) financing activities:    
Common stock dividends (84.1) (83.3)
Preferred dividends paid by subsidiaries (2.5) (2.5)
Capital contributions from parent 0 25.0
Net change in commercial paper (25.7) (47.4)
Other (1.3) (7.3)
Net cash flows from (used for) financing activities (113.6) (115.5)
Net increase (decrease) in cash and cash equivalents 13.5 23.4
Cash and cash equivalents at beginning of period 2.7 0.1
Cash and cash equivalents at end of period 16.2 23.5
Supplemental cash flows information:    
Interest, net of capitalized interest 63.1 63.4
Income taxes, net of refunds 7.9 (37.1)
Significant noncash investing and financing activities:    
Accrued capital expenditures 45.0 15.1
Deferred income tax assets [Member]
    
Other changes in assets and liabilities:    
Deferred income taxes (67.2) (0.6)
Deferred income tax assets [Member] | IPL [Member]
    
Other changes in assets and liabilities:    
Deferred income taxes (22.4) 3.1
Deferred income tax assets [Member] | WPL [Member]
    
Other changes in assets and liabilities:    
Deferred income taxes (44.3) (1.3)
Deferred income tax liabilities [Member]
    
Other changes in assets and liabilities:    
Deferred income taxes 157.7 97.4
Deferred income tax liabilities [Member] | IPL [Member]
    
Other changes in assets and liabilities:    
Deferred income taxes 111.3 91.5
Deferred income tax liabilities [Member] | WPL [Member]
    
Other changes in assets and liabilities:    
Deferred income taxes $ 46.6 $ 6.2