Financial Instruments (Fair Value of Financial Instruments) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity investments without readily determinable fair value	$ 414.6	$ 414.7
Noncurrent investments	2,111.4	2,005.4
Carrying Amount
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	806.2	5,727.1
Short-term investments, debt securities	100.7	88.2
Noncurrent investments	2,111.4	2,005.4
Short-term commercial paper borrowings	(2,349.6)	(498.9)
Long-term debt, including current portion	(13,615.5)	(9,799.7)
Cost
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	806.2	5,727.1
Estimate of Fair Value Measurement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	806.2	5,727.1
Short-term commercial paper borrowings	(2,342.3)	(497.6)
Long-term debt, including current portion	(14,238.8)	(9,970.0)
Estimate of Fair Value Measurement | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	806.2	5,727.1
Short-term commercial paper borrowings	0.0	0.0
Long-term debt, including current portion	0.0	0.0
Estimate of Fair Value Measurement | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0.0	0.0
Short-term commercial paper borrowings	(2,342.3)	(497.6)
Long-term debt, including current portion	(14,238.8)	(9,970.0)
Estimate of Fair Value Measurement | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0.0	0.0
Short-term commercial paper borrowings	0.0	0.0
Long-term debt, including current portion	0.0	0.0
U.S. government and agency securities | Carrying Amount
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments, debt securities	13.5	16.9
Noncurrent investments, debt securities	148.0	149.1
U.S. government and agency securities | Cost
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments, debt securities	13.6	17.1
Noncurrent investments, debt securities	150.0	153.6
U.S. government and agency securities | Estimate of Fair Value Measurement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments, debt securities	13.5	16.9
Noncurrent investments, debt securities	148.0	149.1
U.S. government and agency securities | Estimate of Fair Value Measurement | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments, debt securities	13.5	16.9
Noncurrent investments, debt securities	148.0	149.1
U.S. government and agency securities | Estimate of Fair Value Measurement | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments, debt securities	0.0	0.0
Noncurrent investments, debt securities	0.0	0.0
U.S. government and agency securities | Estimate of Fair Value Measurement | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments, debt securities	0.0	0.0
Noncurrent investments, debt securities	0.0	0.0
Corporate debt securities | Carrying Amount
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments, debt securities	81.7	62.2
Noncurrent investments, debt securities	533.6	568.0
Corporate debt securities | Cost
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments, debt securities	81.7	62.6
Noncurrent investments, debt securities	535.2	587.8
Corporate debt securities | Estimate of Fair Value Measurement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments, debt securities	81.7	62.2
Noncurrent investments, debt securities	533.6	568.0
Corporate debt securities | Estimate of Fair Value Measurement | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments, debt securities	0.0	0.0
Noncurrent investments, debt securities	0.0	0.0
Corporate debt securities | Estimate of Fair Value Measurement | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments, debt securities	81.7	62.2
Noncurrent investments, debt securities	533.6	568.0
Corporate debt securities | Estimate of Fair Value Measurement | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments, debt securities	0.0	0.0
Noncurrent investments, debt securities	0.0	0.0
Mortgage-backed securities | Carrying Amount
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Noncurrent investments, debt securities	118.7	111.4
Mortgage-backed securities | Cost
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Noncurrent investments, debt securities	119.9	114.5
Mortgage-backed securities | Estimate of Fair Value Measurement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Noncurrent investments, debt securities	118.7	111.4
Mortgage-backed securities | Estimate of Fair Value Measurement | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Noncurrent investments, debt securities	0.0	0.0
Mortgage-backed securities | Estimate of Fair Value Measurement | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Noncurrent investments, debt securities	118.7	111.4
Mortgage-backed securities | Estimate of Fair Value Measurement | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Noncurrent investments, debt securities	0.0	0.0
Asset-backed securities | Carrying Amount
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments, debt securities	4.0	7.6
Noncurrent investments, debt securities	36.2	27.7
Asset-backed securities | Cost
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments, debt securities	4.0	7.7
Noncurrent investments, debt securities	36.2	27.9
Asset-backed securities | Estimate of Fair Value Measurement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments, debt securities	4.0	7.6
Noncurrent investments, debt securities	36.2	27.7
Asset-backed securities | Estimate of Fair Value Measurement | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments, debt securities	0.0	0.0
Noncurrent investments, debt securities	0.0	0.0
Asset-backed securities | Estimate of Fair Value Measurement | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments, debt securities	4.0	7.6
Noncurrent investments, debt securities	36.2	27.7
Asset-backed securities | Estimate of Fair Value Measurement | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments, debt securities	0.0	0.0
Noncurrent investments, debt securities	0.0	0.0
Other securities | Carrying Amount
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments, debt securities	1.5	1.5
Other securities | Cost
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments, debt securities	1.5	1.5
Other securities | Estimate of Fair Value Measurement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments, debt securities	1.5	1.5
Other securities | Estimate of Fair Value Measurement | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments, debt securities	0.0	0.0
Other securities | Estimate of Fair Value Measurement | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments, debt securities	1.5	1.5
Other securities | Estimate of Fair Value Measurement | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments, debt securities	0.0	0.0
Other securities | Carrying Amount
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	82.4	87.8
Other securities | Cost
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	29.7	29.7
Other securities | Estimate of Fair Value Measurement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	82.4	87.8
Other securities | Estimate of Fair Value Measurement | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	0.0	0.0
Other securities | Estimate of Fair Value Measurement | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	0.0	0.0
Other securities | Estimate of Fair Value Measurement | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	82.4	87.8
Marketable equity securities | Carrying Amount
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	502.1	357.5
Marketable equity securities | Cost
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	238.7	238.3
Marketable equity securities | Estimate of Fair Value Measurement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	502.1	357.5
Marketable equity securities | Estimate of Fair Value Measurement | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	502.1	357.5
Marketable equity securities | Estimate of Fair Value Measurement | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	0.0	0.0
Marketable equity securities | Estimate of Fair Value Measurement | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	0.0	0.0
Equity method investments | Carrying Amount
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity method investments	$ 275.8	$ 289.2