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Fair Value - Recurring Fair Value Measures (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2015 | Dec. 31, 2014
Investments [Abstract] |  |  |  |  |
Cash Equivalents |  | $ 2.0 |  | $ 2.9 |
Liabilities [Abstract] |  |  |  |  |
U.S. Water Services Contingent Consideration | [1] | 36.6 |  | 0.0 |
Recurring Fair Value Measures [Member] |  |  |  |  |
Investments [Abstract] |  |  |  |  |
Available-for-sale - Equity Securities |  | 7.6 | [2] | 8.1 | [3]
Available-for-sale - Corporate Debt Securities |  | 10.9 | [2] | 10.8 | [3]
Cash Equivalents |  | 2.0 | [2] | 2.9 | [3]
Total Fair Value of Assets |  | 20.5 |  | 21.8 |
Liabilities [Abstract] |  |  |  |  |
Deferred Compensation |  | 16.1 | [4] | 16.2 | [5]
Derivatives – Interest Rate Swap | [6] |  |  | 0.3 |
U.S. Water Services Contingent Consideration | [4] | 36.6 |  |  |
Total Fair Value of Liabilities |  | 52.7 |  | 16.5 |
Total Net Fair Value of Assets (Liabilities) |  | (32.2) |  | 5.3 |
Activity in Level 3 [Roll Forward] |  |  |  |  |
Fair Value Hierarchy Transfers, All Levels |  |  |  | 0.0 |
Recurring Fair Value Measures [Member] | Level 1 [Member] |  |  |  |  |
Investments [Abstract] |  |  |  |  |
Available-for-sale - Equity Securities |  | 7.6 | [2] | 8.1 | [3]
Available-for-sale - Corporate Debt Securities |  | 0.0 | [2] | 0.0 | [3]
Cash Equivalents |  | 2.0 | [2] | 2.9 | [3]
Total Fair Value of Assets |  | 9.6 |  | 11.0 |
Liabilities [Abstract] |  |  |  |  |
Deferred Compensation |  | 0.0 | [4] | 0.0 | [5]
Derivatives – Interest Rate Swap | [6] |  |  | 0.0 |
U.S. Water Services Contingent Consideration | [4] | 0.0 |  |  |
Total Fair Value of Liabilities |  | 0.0 |  | 0.0 |
Total Net Fair Value of Assets (Liabilities) |  | 9.6 |  | 11.0 |
Recurring Fair Value Measures [Member] | Level 2 [Member] |  |  |  |  |
Investments [Abstract] |  |  |  |  |
Available-for-sale - Equity Securities |  | 0.0 | [2] | 0.0 | [3]
Available-for-sale - Corporate Debt Securities |  | 10.9 | [2] | 10.8 | [3]
Cash Equivalents |  | 0.0 | [2] | 0.0 | [3]
Total Fair Value of Assets |  | 10.9 |  | 10.8 |
Liabilities [Abstract] |  |  |  |  |
Deferred Compensation |  | 16.1 | [4] | 16.2 | [5]
Derivatives – Interest Rate Swap | [6] |  |  | 0.3 |
U.S. Water Services Contingent Consideration | [4] | 0.0 |  |  |
Total Fair Value of Liabilities |  | 16.1 |  | 16.5 |
Total Net Fair Value of Assets (Liabilities) |  | (5.2) |  | (5.7) |
Recurring Fair Value Measures [Member] | Level 3 [Member] |  |  |  |  |
Investments [Abstract] |  |  |  |  |
Available-for-sale - Equity Securities |  | 0.0 | [2] | 0.0 | [3]
Available-for-sale - Corporate Debt Securities |  | 0.0 | [2] | 0.0 | [3]
Cash Equivalents |  | 0.0 | [2] | 0.0 | [3]
Total Fair Value of Assets |  | 0.0 |  | 0.0 |
Liabilities [Abstract] |  |  |  |  |
Deferred Compensation |  | 0.0 | [4] | 0.0 | [5]
Derivatives – Interest Rate Swap | [6] |  |  | 0.0 |
U.S. Water Services Contingent Consideration | [4] | 36.6 |  |  |
Total Fair Value of Liabilities |  | 36.6 |  | 0.0 |
Total Net Fair Value of Assets (Liabilities) |  | (36.6) |  | 0.0 |
Activity in Level 3 [Roll Forward] |  |  |  |  |
Balance as of December 31, 2014 |  | 0.0 |  |  |
Activity in Level 3 |  | 0.0 |  |  |
Balance as of December 31, 2015 |  | 36.6 |  | $ 0.0 |
Recurring Fair Value Measures [Member] | Level 3 [Member] | Recognition of U.S. Water Services Contingent Consideration [Member] |  |  |  |  |
Activity in Level 3 [Roll Forward] |  |  |  |  |
Activity in Level 3 |  | 35.7 |  |  |
Recurring Fair Value Measures [Member] | Level 3 [Member] | Accretion Expense [Member] |  |  |  |  |
Activity in Level 3 [Roll Forward] |  |  |  |  |
Activity in Level 3 | [7] | 2.4 |  |  |
Recurring Fair Value Measures [Member] | Level 3 [Member] | Changes in Cash Flow Projections [Member] |  |  |  |  |
Activity in Level 3 [Roll Forward] |  |  |  |  |
Activity in Level 3 |  | $ (1.5) |  |  |
[1] | Contingent Consideration relates to the estimated fair value of the earnings-based payment resulting from the U.S. Water Services acquisition. (See Note 7. Acquisitions and Note 10. Fair Value.)
[2] | Included in Other Investments on the Consolidated Balance Sheet.
[3] | Included in Other Investments on the Consolidated Balance Sheet.
[4] | Included in Other Non-Current Liabilities on the Consolidated Balance Sheet.
[5] | Included in Other Non-Current Liabilities on the Consolidated Balance Sheet.
[6] | Included in Current Liabilities - Other on the Consolidated Balance Sheet.
[7] | Included in Interest Expense on the Consolidated Statement of Income.

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