Fair Value - Recurring Fair Value Measures (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020		Dec. 31, 2019
Liabilities [Abstract]
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, within One Year, Fair Value	$ 1.8
Available-for-sale Securities, Debt Maturities, After One Year Through Three Years, Fair Value	4.3
Available-for-sale Securities, Debt Maturities, After Three Years Through Five Years, Fair Value	4.0
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	7.2	[1]	$ 11.1	[2]
Available-for-sale – Corporate and Governmental Debt Securities	10.4	[1],[3]	9.7	[2]
Cash Equivalents	5.5	[1]	0.9	[2]
Total Fair Value of Assets	23.1		21.7
Liabilities [Abstract]
Deferred Compensation	21.0	[4]	21.2	[5]
Total Fair Value of Liabilities	21.0		21.2
Total Net Fair Value of Assets (Liabilities)	2.1		0.5
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	7.2	[1]	11.1	[2]
Available-for-sale – Corporate and Governmental Debt Securities	0.0	[1],[3]	0.0	[2]
Cash Equivalents	5.5	[1]	0.9	[2]
Total Fair Value of Assets	12.7		12.0
Liabilities [Abstract]
Deferred Compensation	0.0	[4]	0.0	[5]
Total Fair Value of Liabilities	0.0		0.0
Total Net Fair Value of Assets (Liabilities)	12.7		12.0
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	10.4	[1],[3]	9.7	[2]
Cash Equivalents	0.0	[1]	0.0	[2]
Total Fair Value of Assets	10.4		9.7
Liabilities [Abstract]
Deferred Compensation	21.0	[4]	21.2	[5]
Total Fair Value of Liabilities	21.0		21.2
Total Net Fair Value of Assets (Liabilities)	(10.6)		(11.5)
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],[3]	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	[4]	0.0	[5]
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] Included in Other Non-Current Assets on the Consolidated Balance Sheet.

[3] As of December 31, 2020, the aggregate amount of available-for-sale corporate and governmental debt securities maturing in one year or less was $1.8 million, in one year to less than three years was $4.3 million, in three years to less than five years was $4.0 million and in five or more years was $0.3 million.

[4] Included in Other Non-Current Liabilities on the Consolidated Balance Sheet.

[5] Included in Other Non-Current Liabilities on the Consolidated Balance Sheet.