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Fair Value - Recurring Fair Value Measures (Details) - USD ($) $ in Millions | Jun. 30, 2020 | Dec. 31, 2019
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Investments [Abstract] |  |  |  |
Available-for-sale Securities, Debt Maturities, within One Year, Fair Value |  | $ 3.8 |  |
Available-for-sale Securities, Debt Maturities, After One Year Through Three Years, Fair Value |  | 5.0 |  |
Available-for-sale Securities, Debt Maturities, After Three Years Through Five Years, Fair Value |  | 1.0 |  |
Available-for-sale Securities, Debt Maturities, After Five Years, Fair Value |  | 0.0 |  |
Recurring Fair Value Measures [Member] |  |  |  |
Investments [Abstract] |  |  |  |
Available-for-sale – Equity Securities | [1] | 10.1 |  | $ 11.1
Available-for-sale – Corporate and Governmental Debt Securities (b) | [1] | 9.8 | [2] | 9.7
Cash Equivalents | [1] | 0.8 |  | 0.9
Total Fair Value of Assets |  | 20.7 |  | 21.7
Liabilities [Abstract] |  |  |  |
Deferred Compensation | [3] | 20.0 |  | 21.2
Total Fair Value of Liabilities |  | 20.0 |  | 21.2
Total Net Fair Value of Assets (Liabilities) |  | 0.7 |  | 0.5
Recurring Fair Value Measures [Member] | Level 1 [Member] |  |  |  |
Investments [Abstract] |  |  |  |
Available-for-sale – Equity Securities | [1] | 10.1 |  | 11.1
Available-for-sale – Corporate and Governmental Debt Securities (b) | [1] | 0.0 | [2] | 0.0
Cash Equivalents | [1] | 0.8 |  | 0.9
Total Fair Value of Assets |  | 10.9 |  | 12.0
Liabilities [Abstract] |  |  |  |
Deferred Compensation | [3] | 0.0 |  | 0.0
Total Fair Value of Liabilities |  | 0.0 |  | 0.0
Total Net Fair Value of Assets (Liabilities) |  | 10.9 |  | 12.0
Recurring Fair Value Measures [Member] | Level 2 [Member] |  |  |  |
Investments [Abstract] |  |  |  |
Available-for-sale – Equity Securities | [1] | 0.0 |  | 0.0
Available-for-sale – Corporate and Governmental Debt Securities (b) | [1] | 9.8 | [2] | 9.7
Cash Equivalents | [1] | 0.0 |  | 0.0
Total Fair Value of Assets |  | 9.8 |  | 9.7
Liabilities [Abstract] |  |  |  |
Deferred Compensation | [3] | 20.0 |  | 21.2
Total Fair Value of Liabilities |  | 20.0 |  | 21.2
Total Net Fair Value of Assets (Liabilities) |  | (10.2) |  | (11.5)
Recurring Fair Value Measures [Member] | Level 3 [Member] |  |  |  |
Investments [Abstract] |  |  |  |
Available-for-sale – Equity Securities | [1] | 0.0 |  | 0.0
Available-for-sale – Corporate and Governmental Debt Securities (b) | [1] | 0.0 | [2] | 0.0
Cash Equivalents | [1] | 0.0 |  | 0.0
Total Fair Value of Assets |  | 0.0 |  | 0.0
Liabilities [Abstract] |  |  |  |
Deferred Compensation | [3] | 0.0 |  | 0.0
Total Fair Value of Liabilities |  | 0.0 |  | 0.0
Total Net Fair Value of Assets (Liabilities) |  | $ 0.0 |  | $ 0.0
[1] | Included in Other Non-Current Assets on the Consolidated Balance Sheet.
[2] | As of June 30, 2020, the aggregate amount of available-for-sale corporate and governmental debt securities maturing in one year or less was $3.8 million, in one year to less than three years was $5.0 million, in three years to less than five years was $1.0 million and in five or more years was zero.
[3] | Included in Other Non-Current Liabilities on the Consolidated Balance Sheet.

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