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Fair Value - Recurring Fair Value Measures (Details) - USD ($) $ in Millions | Jun. 30, 2021 | Dec. 31, 2020
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Investments [Abstract] |  |  |  |
Available-for-sale Securities, Debt Maturities, within One Year, Fair Value |  | $ 2.0 |  |
Available-for-sale Securities, Debt Maturities, After One Year Through Three Years, Fair Value |  | 2.6 |  |
Available-for-sale Securities, Debt Maturities, After Three Years Through Five Years, Fair Value |  | 3.6 |  |
Available-for-sale Securities, Debt Maturities, After Five Years, Fair Value |  | 0.3 |  |
Recurring Fair Value Measures [Member] |  |  |  |
Investments [Abstract] |  |  |  |
Available-for-sale – Equity Securities | [1] | 9.1 |  | $ 7.2
Available-for-sale – Corporate and Governmental Debt Securities (b) | [1] | 8.5 | [2] | 10.4
Cash Equivalents | [1] | 1.9 |  | 5.5
Total Fair Value of Assets |  | 19.5 |  | 23.1
Liabilities [Abstract] |  |  |  |
Deferred Compensation | [3] | 22.1 |  | 21.0
Total Fair Value of Liabilities |  | 22.1 |  | 21.0
Total Net Fair Value of Assets (Liabilities) |  | (2.6) |  | 2.1
Recurring Fair Value Measures [Member] | Level 1 [Member] |  |  |  |
Investments [Abstract] |  |  |  |
Available-for-sale – Equity Securities | [1] | 9.1 |  | 7.2
Available-for-sale – Corporate and Governmental Debt Securities (b) | [1] | 0.0 | [2] | 0.0
Cash Equivalents | [1] | 1.9 |  | 5.5
Total Fair Value of Assets |  | 11.0 |  | 12.7
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) |  | 11.0 |  | 12.7
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] | 8.5 | [2] | 10.4
Cash Equivalents | [1] | 0.0 |  | 0.0
Total Fair Value of Assets |  | 8.5 |  | 10.4
Liabilities [Abstract] |  |  |  |
Deferred Compensation | [3] | 22.1 |  | 21.0
Total Fair Value of Liabilities |  | 22.1 |  | 21.0
Total Net Fair Value of Assets (Liabilities) |  | (13.6) |  | (10.6)
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, 2021, the aggregate amount of available-for-sale corporate and governmental debt securities maturing in one year or less was $2.0 million, in one year to less than three years was $2.6 million, in three years to less than five years was $3.6 million and in five or more years was $0.3 million.
[3] | Included in Other Non-Current Liabilities on the Consolidated Balance Sheet.

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