Financial Instruments (Schedule of Fair Value Measurement) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Noncurrent investments:
Noncurrent investments	$ 1,962.4	$ 2,005.4
Carrying Amount
Statement [Line Items]
Cash equivalents	1,025.4	5,727.1
Short-term investments:
Debt securities	101.0	88.2
Noncurrent investments:
Equity investments without readily determinable fair values	405.0	414.7
Noncurrent investments	1,962.4	2,005.4
Cost
Statement [Line Items]
Cash equivalents	1,025.4	5,727.1
Fair Value
Statement [Line Items]
Cash equivalents	1,025.4	5,727.1
Fair Value \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Statement [Line Items]
Cash equivalents	1,025.4	5,727.1
Fair Value \| Significant Other Observable Inputs (Level 2)
Statement [Line Items]
Cash equivalents	0.0	0.0
Fair Value \| Significant Unobservable Inputs (Level 3)
Statement [Line Items]
Cash equivalents	0.0	0.0
U.S. government and agency securities \| Carrying Amount
Short-term investments:
Debt securities	7.2	16.9
Noncurrent investments:
Noncurrent investments, debt securities	77.2	149.1
U.S. government and agency securities \| Cost
Short-term investments:
Debt securities	7.2	17.1
Noncurrent investments:
Noncurrent investments, debt securities	76.3	153.6
U.S. government and agency securities \| Fair Value
Short-term investments:
Debt securities	7.2	16.9
Noncurrent investments:
Noncurrent investments, debt securities	77.2	149.1
U.S. government and agency securities \| Fair Value \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Short-term investments:
Debt securities	7.2	16.9
Noncurrent investments:
Noncurrent investments, debt securities	77.2	149.1
U.S. government and agency securities \| Fair Value \| Significant Other Observable Inputs (Level 2)
Short-term investments:
Debt securities	0.0	0.0
Noncurrent investments:
Noncurrent investments, debt securities	0.0	0.0
U.S. government and agency securities \| Fair Value \| Significant Unobservable Inputs (Level 3)
Short-term investments:
Debt securities	0.0	0.0
Noncurrent investments:
Noncurrent investments, debt securities	0.0	0.0
Corporate debt securities \| Carrying Amount
Short-term investments:
Debt securities	81.4	62.2
Noncurrent investments:
Noncurrent investments, debt securities	271.1	568.0
Corporate debt securities \| Cost
Short-term investments:
Debt securities	81.1	62.6
Noncurrent investments:
Noncurrent investments, debt securities	267.8	587.8
Corporate debt securities \| Fair Value
Short-term investments:
Debt securities	81.4	62.2
Noncurrent investments:
Noncurrent investments, debt securities	271.1	568.0
Corporate debt securities \| Fair Value \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Short-term investments:
Debt securities	0.0	0.0
Noncurrent investments:
Noncurrent investments, debt securities	0.0	0.0
Corporate debt securities \| Fair Value \| Significant Other Observable Inputs (Level 2)
Short-term investments:
Debt securities	81.4	62.2
Noncurrent investments:
Noncurrent investments, debt securities	271.1	568.0
Corporate debt securities \| Fair Value \| Significant Unobservable Inputs (Level 3)
Short-term investments:
Debt securities	0.0	0.0
Noncurrent investments:
Noncurrent investments, debt securities	0.0	0.0
Asset-backed securities \| Carrying Amount
Short-term investments:
Debt securities	2.6	7.6
Noncurrent investments:
Noncurrent investments, debt securities	30.0	27.7
Asset-backed securities \| Cost
Short-term investments:
Debt securities	2.6	7.7
Noncurrent investments:
Noncurrent investments, debt securities	29.6	27.9
Asset-backed securities \| Fair Value
Short-term investments:
Debt securities	2.6	7.6
Noncurrent investments:
Noncurrent investments, debt securities	30.0	27.7
Asset-backed securities \| Fair Value \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Short-term investments:
Debt securities	0.0	0.0
Noncurrent investments:
Noncurrent investments, debt securities	0.0	0.0
Asset-backed securities \| Fair Value \| Significant Other Observable Inputs (Level 2)
Short-term investments:
Debt securities	2.6	7.6
Noncurrent investments:
Noncurrent investments, debt securities	30.0	27.7
Asset-backed securities \| Fair Value \| Significant Unobservable Inputs (Level 3)
Short-term investments:
Debt securities	0.0	0.0
Noncurrent investments:
Noncurrent investments, debt securities	0.0	0.0
Other securities \| Carrying Amount
Short-term investments:
Debt securities	9.8	1.5
Other securities \| Cost
Short-term investments:
Debt securities	9.8	1.5
Other securities \| Fair Value
Short-term investments:
Debt securities	9.8	1.5
Other securities \| Fair Value \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Short-term investments:
Debt securities	0.0	0.0
Other securities \| Fair Value \| Significant Other Observable Inputs (Level 2)
Short-term investments:
Debt securities	0.0	1.5
Other securities \| Fair Value \| Significant Unobservable Inputs (Level 3)
Short-term investments:
Debt securities	9.8	0.0
Mortgage-backed securities \| Carrying Amount
Noncurrent investments:
Noncurrent investments, debt securities	101.1	111.4
Mortgage-backed securities \| Cost
Noncurrent investments:
Noncurrent investments, debt securities	99.6	114.5
Mortgage-backed securities \| Fair Value
Noncurrent investments:
Noncurrent investments, debt securities	101.1	111.4
Mortgage-backed securities \| Fair Value \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Noncurrent investments:
Noncurrent investments, debt securities	0.0	0.0
Mortgage-backed securities \| Fair Value \| Significant Other Observable Inputs (Level 2)
Noncurrent investments:
Noncurrent investments, debt securities	101.1	111.4
Mortgage-backed securities \| Fair Value \| Significant Unobservable Inputs (Level 3)
Noncurrent investments:
Noncurrent investments, debt securities	0.0	0.0
Other securities \| Carrying Amount
Noncurrent investments:
Equity securities	60.0	87.8
Other securities \| Cost
Noncurrent investments:
Equity securities	27.4	29.7
Other securities \| Fair Value
Noncurrent investments:
Equity securities	60.0	87.8
Other securities \| Fair Value \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Noncurrent investments:
Equity securities	0.0	0.0
Other securities \| Fair Value \| Significant Other Observable Inputs (Level 2)
Noncurrent investments:
Equity securities	0.0	0.0
Other securities \| Fair Value \| Significant Unobservable Inputs (Level 3)
Noncurrent investments:
Equity securities	60.0	87.8
Marketable equity securities \| Carrying Amount
Noncurrent investments:
Equity securities	718.6	357.5
Marketable equity securities \| Cost
Noncurrent investments:
Equity securities	254.4	238.3
Marketable equity securities \| Fair Value
Noncurrent investments:
Equity securities	718.6	357.5
Marketable equity securities \| Fair Value \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Noncurrent investments:
Equity securities	718.6	357.5
Marketable equity securities \| Fair Value \| Significant Other Observable Inputs (Level 2)
Noncurrent investments:
Equity securities	0.0	0.0
Marketable equity securities \| Fair Value \| Significant Unobservable Inputs (Level 3)
Noncurrent investments:
Equity securities	0.0	0.0
Equity method investments \| Carrying Amount
Noncurrent investments:
Equity method investments	$ 299.4	$ 289.2

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