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Fair Value - Recurring Fair Value Measures (Details) - USD ($) $ in Millions | 9 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2017 | Dec. 31, 2016
Investments [Abstract] |  |  |  |  |
Cash Equivalents |  | $ 2.2 |  | $ 1.3 |
Recurring Fair Value Measures [Member] |  |  |  |  |
Investments [Abstract] |  |  |  |  |
Available-for-sale – Equity Securities |  | 10.9 | [1] | 7.1 | [2]
Available-for-sale – Corporate and Governmental Debt Securities |  | 10.1 | [1] | 11.7 | [2]
Cash Equivalents |  | 2.2 | [1] | 1.3 | [2]
Total Fair Value of Assets |  | 23.2 |  | 20.1 |
Liabilities [Abstract] |  |  |  |  |
Deferred Compensation |  | 18.7 | [3] | 16.0 | [4]
U.S. Water Services Contingent Consideration |  | 5.6 | [3] | 25.0 | [4]
Total Fair Value of Liabilities |  | 24.3 |  | 41.0 |
Total Net Fair Value of Assets (Liabilities) |  | (1.1) |  | (20.9) |
Fair Value Hierarchy Transfers, All Levels |  | 0.0 |  | 0.0 |
Recurring Fair Value Measures [Member] | Level 1 [Member] |  |  |  |  |
Investments [Abstract] |  |  |  |  |
Available-for-sale – Equity Securities |  | 10.9 | [1] | 7.1 | [2]
Available-for-sale – Corporate and Governmental Debt Securities |  | 0.0 | [1] | 0.0 | [2]
Cash Equivalents |  | 2.2 | [1] | 1.3 | [2]
Total Fair Value of Assets |  | 13.1 |  | 8.4 |
Liabilities [Abstract] |  |  |  |  |
Deferred Compensation |  | 0.0 | [3] | 0.0 | [4]
U.S. Water Services Contingent Consideration |  | 0.0 | [3] | 0.0 | [4]
Total Fair Value of Liabilities |  | 0.0 |  | 0.0 |
Total Net Fair Value of Assets (Liabilities) |  | 13.1 |  | 8.4 |
Recurring Fair Value Measures [Member] | Level 2 [Member] |  |  |  |  |
Investments [Abstract] |  |  |  |  |
Available-for-sale – Equity Securities |  | 0.0 | [1] | 0.0 | [2]
Available-for-sale – Corporate and Governmental Debt Securities |  | 10.1 | [1] | 11.7 | [2]
Cash Equivalents |  | 0.0 | [1] | 0.0 | [2]
Total Fair Value of Assets |  | 10.1 |  | 11.7 |
Liabilities [Abstract] |  |  |  |  |
Deferred Compensation |  | 18.7 | [3] | 16.0 | [4]
U.S. Water Services Contingent Consideration |  | 0.0 | [3] | 0.0 | [4]
Total Fair Value of Liabilities |  | 18.7 |  | 16.0 |
Total Net Fair Value of Assets (Liabilities) |  | (8.6) |  | (4.3) |
Recurring Fair Value Measures [Member] | Level 3 [Member] |  |  |  |  |
Investments [Abstract] |  |  |  |  |
Available-for-sale – Equity Securities |  | 0.0 | [1] | 0.0 | [2]
Available-for-sale – Corporate and Governmental Debt Securities |  | 0.0 | [1] | 0.0 | [2]
Cash Equivalents |  | 0.0 | [1] | 0.0 | [2]
Total Fair Value of Assets |  | 0.0 |  | 0.0 |
Liabilities [Abstract] |  |  |  |  |
Deferred Compensation |  | 0.0 | [3] | 0.0 | [4]
U.S. Water Services Contingent Consideration |  | 5.6 | [3] | 25.0 | [4]
Total Fair Value of Liabilities |  | 5.6 |  | 25.0 |
Total Net Fair Value of Assets (Liabilities) |  | (5.6) |  | (25.0) |
Activity in Level 3 [Roll Forward] |  |  |  |  |
Beginning Balance |  | 25.0 |  |  |
Ending Balance |  | 5.6 |  | $ 25.0 |
Recurring Fair Value Measures [Member] | Level 3 [Member] | Accretion [Member] |  |  |  |  |
Activity in Level 3 [Roll Forward] |  |  |  |  |
Activity in Level 3 |  | 0.7 |  |  |
Recurring Fair Value Measures [Member] | Level 3 [Member] | Payments [Member] |  |  |  |  |
Activity in Level 3 [Roll Forward] |  |  |  |  |
Activity in Level 3 | [5] | (19.7) |  |  |
Recurring Fair Value Measures [Member] | Level 3 [Member] | Changes in Cash Flow Projections [Member] |  |  |  |  |
Activity in Level 3 [Roll Forward] |  |  |  |  |
Activity in Level 3 |  | $ (0.4) |  |  |
[1] | Included in Other Investments on the Consolidated Balance Sheet.
[2] | Included in Other Investments on the Consolidated Balance Sheet.
[3] | Included in Other Non-Current Liabilities on the Consolidated Balance Sheet
[4] | Included in Other Non-Current Liabilities on the Consolidated Balance Sheet.
[5] | Payments and changes in cash flow projections reflect the impact of a modification to the shareholder agreement in the first quarter of 2017 which provided participants a one-time election to sell shares at a determined price. Participants representing approximately half of the outstanding contingent consideration shares made the election, and were paid in the first half of 2017.

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