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Fair Value - Recurring Fair Value Measures (Details) - USD ($) $ in Millions | Mar. 31, 2021 | Dec. 31, 2020
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Investments [Abstract] |  |  |  |
Available-for-sale Securities, Debt Maturities, within One Year, Fair Value |  | $ 2.5 |  |
Available-for-sale Securities, Debt Maturities, After One Year Through Three Years, Fair Value |  | 2.8 |  |
Available-for-sale Securities, Debt Maturities, After Three Years Through Five Years, Fair Value |  | 3.7 |  |
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] | 7.8 |  | $ 7.2
Available-for-sale – Corporate and Governmental Debt Securities (b) | [1] | 9.3 | [2] | 10.4
Cash Equivalents | [1] | 1.7 |  | 5.5
Total Fair Value of Assets |  | 18.8 |  | 23.1
Liabilities [Abstract] |  |  |  |
Deferred Compensation | [3] | 21.0 |  | 21.0
Total Fair Value of Liabilities |  | 21.0 |  | 21.0
Total Net Fair Value of Assets (Liabilities) |  | (2.2) |  | 2.1
Recurring Fair Value Measures [Member] | Level 1 [Member] |  |  |  |
Investments [Abstract] |  |  |  |
Available-for-sale – Equity Securities | [1] | 7.8 |  | 7.2
Available-for-sale – Corporate and Governmental Debt Securities (b) | [1] | 0.0 | [2] | 0.0
Cash Equivalents | [1] | 1.7 |  | 5.5
Total Fair Value of Assets |  | 9.5 |  | 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) |  | 9.5 |  | 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] | 9.3 | [2] | 10.4
Cash Equivalents | [1] | 0.0 |  | 0.0
Total Fair Value of Assets |  | 9.3 |  | 10.4
Liabilities [Abstract] |  |  |  |
Deferred Compensation | [3] | 21.0 |  | 21.0
Total Fair Value of Liabilities |  | 21.0 |  | 21.0
Total Net Fair Value of Assets (Liabilities) |  | (11.7) |  | (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 March 31, 2021, the aggregate amount of available-for-sale corporate and governmental debt securities maturing in one year or less was $2.5 million, in one year to less than three years was $2.8 million, in three years to less than five years was $3.7 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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- Definition Amount of available-for-sale debt securities at fair value maturing in after the fifth fiscal year following the latest fiscal year (maturing in five years or more). + References No definition available. + Details
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- Definition Amount of available-for-sale debt securities at fair value maturing after the first fiscal year through the third fiscal year following the latest fiscal year (maturing in more than one year to less than three years). + References No definition available. + Details
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