Fair Value - Recurring Fair Value Measures (Details) - USD ($) $ in Millions		Sep. 30, 2020		Dec. 31, 2019
Investments [Abstract]
Available-for-sale Securities, Debt Maturities, within One Year, Fair Value		$ 2.6
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		3.3
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]	10.4		$ 11.1
Available-for-sale – Corporate and Governmental Debt Securities (b)	[1]	10.5	[2]	9.7
Cash Equivalents	[1]	1.3		0.9
Total Fair Value of Assets		22.2		21.7
Liabilities [Abstract]
Deferred Compensation	[3]	21.3		21.2
Total Fair Value of Liabilities		21.3		21.2
Total Net Fair Value of Assets (Liabilities)		0.9		0.5
Recurring Fair Value Measures [Member] | Level 1 [Member]
Investments [Abstract]
Available-for-sale – Equity Securities	[1]	10.4		11.1
Available-for-sale – Corporate and Governmental Debt Securities (b)	[1]	0.0	[2]	0.0
Cash Equivalents	[1]	1.3		0.9
Total Fair Value of Assets		11.7		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)		11.7		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]	10.5	[2]	9.7
Cash Equivalents	[1]	0.0		0.0
Total Fair Value of Assets		10.5		9.7
Liabilities [Abstract]
Deferred Compensation	[3]	21.3		21.2
Total Fair Value of Liabilities		21.3		21.2
Total Net Fair Value of Assets (Liabilities)		(10.8)		(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 September 30, 2020, the aggregate amount of available-for-sale corporate and governmental debt securities maturing in one year or less was $2.6 million, in one year to less than three years was $4.3 million, in three years to less than five years was $3.3 million and in five or more years was $0.3 million.

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