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Condensed Parent Company Financial Statements (Condensed Statements of Cash Flow) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013
Net cash flows from operating activities | $ 871.2 | $ 891.6 | $ 731.0
Cash flows used for investing activities: |  |  |
Other | (24.8) | (14.9) | (18.8)
Net cash flows used for investing activities | (919.2) | (917.7) | (754.7)
Cash flows used for financing activities: |  |  |
Common stock dividends | (247.3) | (225.8) | (208.3)
Proceeds from issuance of common stock, net | 151.2 | 0.0 | 0.0
Proceeds from issuance of long-term debt | 250.7 | 812.9 | 250.0
Payments to retire long-term debt | (183.0) | (358.5) | (1.5)
Net change in commercial paper | 18.5 | (138.1) | 11.9
Other | 6.8 | (17.3) | (28.8)
Net cash flows from (used for) financing activities | (3.1) | 73.2 | 12.3
Net increase (decrease) in cash and cash equivalents | (51.1) | 47.1 | (11.4)
Cash and cash equivalents at beginning of period | 56.9 | 9.8 | 21.2
Cash and cash equivalents at end of period | 5.8 | 56.9 | 9.8
Supplemental cash flows information: |  |  |
Interest, net of capitalized interest | (184.8) | (180.8) | (171.7)
Income taxes, net | 0.0 | 5.3 | 9.6
Parent Company [Member] |  |  |
Net cash flows from operating activities | 262.0 | 246.0 | 238.0
Cash flows used for investing activities: |  |  |
Capital contributions to consolidated subsidiaries | (165.0) | (90.0) | (120.0)
Captial repayments from consolidated subsidiaries | 0.0 | 50.0 | 95.0
Net change in notes receivable from affiliates | 2.0 | (23.0) | 5.0
Other | 0.0 | 0.0 | (2.0)
Net cash flows used for investing activities | (163.0) | (63.0) | (22.0)
Cash flows used for financing activities: |  |  |
Common stock dividends | (247.0) | (226.0) | (208.0)
Proceeds from issuance of common stock, net | 151.0 | 0.0 | 0.0
Proceeds from issuance of long-term debt | 0.0 | 250.0 | 0.0
Payments to retire long-term debt | 0.0 | (250.0) | 0.0
Net change in commercial paper | (1.0) | 45.0 | (9.0)
Other | (2.0) | (2.0) | 1.0
Net cash flows from (used for) financing activities | (99.0) | (183.0) | (216.0)
Net increase (decrease) in cash and cash equivalents | 0.0 | 0.0 | 0.0
Cash and cash equivalents at beginning of period | 0.0 | 0.0 | 0.0
Cash and cash equivalents at end of period | 0.0 | 0.0 | 0.0
Supplemental cash flows information: |  |  |
Interest, net of capitalized interest | (3.0) | (11.0) | (13.0)
Income taxes, net | $ (9.0) | $ (5.0) | $ (7.0)

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