Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Available-for-sale debt securities:
Available-for-sale debt securities	$ 976.3	$ 1,451.5
Derivative assets:
Derivative assets:	90.9	89.0
Cash equivalents
Available-for-sale debt securities:
Available-for-sale debt securities	93.7	333.7
Short-term investments
Available-for-sale debt securities:
Available-for-sale debt securities	328.3	405.5
Long-term investments
Available-for-sale debt securities:
Available-for-sale debt securities	493.2	656.6
Asset-backed securities
Available-for-sale debt securities:
Available-for-sale debt securities	90.8	76.7
Certificates of deposit
Available-for-sale debt securities:
Available-for-sale debt securities	15.3	32.9
Commercial paper
Available-for-sale debt securities:
Available-for-sale debt securities	78.2	89.3
Corporate debt securities
Available-for-sale debt securities:
Available-for-sale debt securities	485.4	637.4
Foreign government debt securities
Available-for-sale debt securities:
Available-for-sale debt securities	7.6	4.6
Time deposits
Available-for-sale debt securities:
Available-for-sale debt securities	64.2	255.6
U.S. government agency securities
Available-for-sale debt securities:
Available-for-sale debt securities	26.7	65.5
U.S. government securities
Available-for-sale debt securities:
Available-for-sale debt securities	147.0	233.8
Privately-held debt and redeemable preferred stock securities
Available-for-sale debt securities:
Available-for-sale debt securities	61.1	55.7
Money market funds
Equity securities:
Equity securities	387.1	536.6
Publicly-traded equity securities
Equity securities:
Equity securities	7.2	6.6
Fair Value, Measurements, Recurring
Available-for-sale debt securities:
Available-for-sale debt securities	976.3	1,451.5
Equity securities:
Equity securities	426.2	572.5
Derivative assets:
Derivative assets:	90.9	89.0
Total assets measured at fair value on a recurring basis	1,493.4	2,113.0
Liabilities:
Derivative liabilities:	(5.9)	(0.5)
Total liabilities measured at fair value on a recurring basis	(5.9)	(0.5)
Fair Value, Measurements, Recurring | Cash equivalents
Derivative assets:
Total assets measured at fair value on a recurring basis	464.0	853.5
Fair Value, Measurements, Recurring | Short-term investments
Derivative assets:
Total assets measured at fair value on a recurring basis	335.5	412.1
Fair Value, Measurements, Recurring | Long-term investments
Derivative assets:
Total assets measured at fair value on a recurring basis	493.2	656.6
Fair Value, Measurements, Recurring | Prepaid expenses and other current assets
Derivative assets:
Total assets measured at fair value on a recurring basis	33.0	37.9
Fair Value, Measurements, Recurring | Other long-term assets
Derivative assets:
Total assets measured at fair value on a recurring basis	167.7	152.9
Fair Value, Measurements, Recurring | Other accrued liabilities
Liabilities:
Total liabilities measured at fair value on a recurring basis	(2.9)	(0.3)
Fair Value, Measurements, Recurring | Other long-term liabilities
Liabilities:
Total liabilities measured at fair value on a recurring basis	(3.0)	(0.2)
Fair Value, Measurements, Recurring | Foreign exchange contracts
Derivative assets:
Derivative assets:	29.2	38.0
Liabilities:
Derivative liabilities:	(5.9)	(0.5)
Fair Value, Measurements, Recurring | Interest rate contracts
Derivative assets:
Derivative assets:	61.7	51.0
Fair Value, Measurements, Recurring | Asset-backed securities
Available-for-sale debt securities:
Available-for-sale debt securities	90.8	76.7
Fair Value, Measurements, Recurring | Certificates of deposit
Available-for-sale debt securities:
Available-for-sale debt securities	15.3	32.9
Fair Value, Measurements, Recurring | Commercial paper
Available-for-sale debt securities:
Available-for-sale debt securities	78.2	89.3
Fair Value, Measurements, Recurring | Corporate debt securities
Available-for-sale debt securities:
Available-for-sale debt securities	485.4	637.4
Fair Value, Measurements, Recurring | Foreign government debt securities
Available-for-sale debt securities:
Available-for-sale debt securities	7.6	4.6
Fair Value, Measurements, Recurring | Time deposits
Available-for-sale debt securities:
Available-for-sale debt securities	64.2	255.6
Fair Value, Measurements, Recurring | U.S. government agency securities
Available-for-sale debt securities:
Available-for-sale debt securities	26.7	65.5
Fair Value, Measurements, Recurring | U.S. government securities
Available-for-sale debt securities:
Available-for-sale debt securities	147.0	233.8
Fair Value, Measurements, Recurring | Privately-held debt and redeemable preferred stock securities
Available-for-sale debt securities:
Available-for-sale debt securities	61.1	55.7
Fair Value, Measurements, Recurring | Money market funds
Equity securities:
Equity securities	387.1	536.6
Fair Value, Measurements, Recurring | Mutual funds
Equity securities:
Equity securities	31.9	29.3
Fair Value, Measurements, Recurring | Publicly-traded equity securities
Equity securities:
Equity securities	7.2	6.6
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets For Identical Assets (Level 1)
Available-for-sale debt securities:
Available-for-sale debt securities	102.9	140.0
Equity securities:
Equity securities	426.2	572.5
Derivative assets:
Derivative assets:	0.0	0.0
Total assets measured at fair value on a recurring basis	529.1	712.5
Liabilities:
Derivative liabilities:	0.0	0.0
Total liabilities measured at fair value on a recurring basis	0.0	0.0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets For Identical Assets (Level 1) | Cash equivalents
Derivative assets:
Total assets measured at fair value on a recurring basis	370.3	519.8
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets For Identical Assets (Level 1) | Short-term investments
Derivative assets:
Total assets measured at fair value on a recurring basis	85.7	101.0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets For Identical Assets (Level 1) | Long-term investments
Derivative assets:
Total assets measured at fair value on a recurring basis	24.4	45.6
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets For Identical Assets (Level 1) | Prepaid expenses and other current assets
Derivative assets:
Total assets measured at fair value on a recurring basis	10.5	9.9
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets For Identical Assets (Level 1) | Other long-term assets
Derivative assets:
Total assets measured at fair value on a recurring basis	38.2	36.2
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets For Identical Assets (Level 1) | Other accrued liabilities
Liabilities:
Total liabilities measured at fair value on a recurring basis	0.0	0.0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets For Identical Assets (Level 1) | Other long-term liabilities
Liabilities:
Total liabilities measured at fair value on a recurring basis	0.0	0.0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets For Identical Assets (Level 1) | Foreign exchange contracts
Derivative assets:
Derivative assets:	0.0	0.0
Liabilities:
Derivative liabilities:	0.0	0.0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets For Identical Assets (Level 1) | Interest rate contracts
Derivative assets:
Derivative assets:	0.0	0.0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets For Identical Assets (Level 1) | Asset-backed securities
Available-for-sale debt securities:
Available-for-sale debt securities	0.0	0.0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets For Identical Assets (Level 1) | Certificates of deposit
Available-for-sale debt securities:
Available-for-sale debt securities	0.0	0.0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets For Identical Assets (Level 1) | Commercial paper
Available-for-sale debt securities:
Available-for-sale debt securities	0.0	0.0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets For Identical Assets (Level 1) | Corporate debt securities
Available-for-sale debt securities:
Available-for-sale debt securities	0.0	0.0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets For Identical Assets (Level 1) | Foreign government debt securities
Available-for-sale debt securities:
Available-for-sale debt securities	0.0	0.0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets For Identical Assets (Level 1) | Time deposits
Available-for-sale debt securities:
Available-for-sale debt securities	0.0	0.0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets For Identical Assets (Level 1) | U.S. government agency securities
Available-for-sale debt securities:
Available-for-sale debt securities	0.0	0.0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets For Identical Assets (Level 1) | U.S. government securities
Available-for-sale debt securities:
Available-for-sale debt securities	102.9	140.0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets For Identical Assets (Level 1) | Privately-held debt and redeemable preferred stock securities
Available-for-sale debt securities:
Available-for-sale debt securities	0.0	0.0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets For Identical Assets (Level 1) | Money market funds
Equity securities:
Equity securities	387.1	536.6
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets For Identical Assets (Level 1) | Mutual funds
Equity securities:
Equity securities	31.9	29.3
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets For Identical Assets (Level 1) | Publicly-traded equity securities
Equity securities:
Equity securities	7.2	6.6
Fair Value, Measurements, Recurring | Significant Other Observable Remaining Inputs (Level 2)
Available-for-sale debt securities:
Available-for-sale debt securities	812.3	1,255.8
Equity securities:
Equity securities	0.0	0.0
Derivative assets:
Derivative assets:	90.9	89.0
Total assets measured at fair value on a recurring basis	903.2	1,344.8
Liabilities:
Derivative liabilities:	(5.9)	(0.5)
Total liabilities measured at fair value on a recurring basis	(5.9)	(0.5)
Fair Value, Measurements, Recurring | Significant Other Observable Remaining Inputs (Level 2) | Cash equivalents
Derivative assets:
Total assets measured at fair value on a recurring basis	93.7	333.7
Fair Value, Measurements, Recurring | Significant Other Observable Remaining Inputs (Level 2) | Short-term investments
Derivative assets:
Total assets measured at fair value on a recurring basis	249.8	311.1
Fair Value, Measurements, Recurring | Significant Other Observable Remaining Inputs (Level 2) | Long-term investments
Derivative assets:
Total assets measured at fair value on a recurring basis	468.8	611.0
Fair Value, Measurements, Recurring | Significant Other Observable Remaining Inputs (Level 2) | Prepaid expenses and other current assets
Derivative assets:
Total assets measured at fair value on a recurring basis	22.5	28.0
Fair Value, Measurements, Recurring | Significant Other Observable Remaining Inputs (Level 2) | Other long-term assets
Derivative assets:
Total assets measured at fair value on a recurring basis	68.4	61.0
Fair Value, Measurements, Recurring | Significant Other Observable Remaining Inputs (Level 2) | Other accrued liabilities
Liabilities:
Total liabilities measured at fair value on a recurring basis	(2.9)	(0.3)
Fair Value, Measurements, Recurring | Significant Other Observable Remaining Inputs (Level 2) | Other long-term liabilities
Liabilities:
Total liabilities measured at fair value on a recurring basis	(3.0)	(0.2)
Fair Value, Measurements, Recurring | Significant Other Observable Remaining Inputs (Level 2) | Foreign exchange contracts
Derivative assets:
Derivative assets:	29.2	38.0
Liabilities:
Derivative liabilities:	(5.9)	(0.5)
Fair Value, Measurements, Recurring | Significant Other Observable Remaining Inputs (Level 2) | Interest rate contracts
Derivative assets:
Derivative assets:	61.7	51.0
Fair Value, Measurements, Recurring | Significant Other Observable Remaining Inputs (Level 2) | Asset-backed securities
Available-for-sale debt securities:
Available-for-sale debt securities	90.8	76.7
Fair Value, Measurements, Recurring | Significant Other Observable Remaining Inputs (Level 2) | Certificates of deposit
Available-for-sale debt securities:
Available-for-sale debt securities	15.3	32.9
Fair Value, Measurements, Recurring | Significant Other Observable Remaining Inputs (Level 2) | Commercial paper
Available-for-sale debt securities:
Available-for-sale debt securities	78.2	89.3
Fair Value, Measurements, Recurring | Significant Other Observable Remaining Inputs (Level 2) | Corporate debt securities
Available-for-sale debt securities:
Available-for-sale debt securities	485.4	637.4
Fair Value, Measurements, Recurring | Significant Other Observable Remaining Inputs (Level 2) | Foreign government debt securities
Available-for-sale debt securities:
Available-for-sale debt securities	7.6	4.6
Fair Value, Measurements, Recurring | Significant Other Observable Remaining Inputs (Level 2) | Time deposits
Available-for-sale debt securities:
Available-for-sale debt securities	64.2	255.6
Fair Value, Measurements, Recurring | Significant Other Observable Remaining Inputs (Level 2) | U.S. government agency securities
Available-for-sale debt securities:
Available-for-sale debt securities	26.7	65.5
Fair Value, Measurements, Recurring | Significant Other Observable Remaining Inputs (Level 2) | U.S. government securities
Available-for-sale debt securities:
Available-for-sale debt securities	44.1	93.8
Fair Value, Measurements, Recurring | Significant Other Observable Remaining Inputs (Level 2) | Privately-held debt and redeemable preferred stock securities
Available-for-sale debt securities:
Available-for-sale debt securities	0.0	0.0
Fair Value, Measurements, Recurring | Significant Other Observable Remaining Inputs (Level 2) | Money market funds
Equity securities:
Equity securities	0.0	0.0
Fair Value, Measurements, Recurring | Significant Other Observable Remaining Inputs (Level 2) | Mutual funds
Equity securities:
Equity securities	0.0	0.0
Fair Value, Measurements, Recurring | Significant Other Observable Remaining Inputs (Level 2) | Publicly-traded equity securities
Equity securities:
Equity securities	0.0	0.0
Fair Value, Measurements, Recurring | Significant Other Unobservable Remaining Inputs (Level 3)
Available-for-sale debt securities:
Available-for-sale debt securities	61.1	55.7
Equity securities:
Equity securities	0.0	0.0
Derivative assets:
Derivative assets:	0.0	0.0
Total assets measured at fair value on a recurring basis	61.1	55.7
Liabilities:
Derivative liabilities:	0.0	0.0
Total liabilities measured at fair value on a recurring basis	0.0	0.0
Fair Value, Measurements, Recurring | Significant Other Unobservable Remaining Inputs (Level 3) | Cash equivalents
Derivative assets:
Total assets measured at fair value on a recurring basis	0.0	0.0
Fair Value, Measurements, Recurring | Significant Other Unobservable Remaining Inputs (Level 3) | Short-term investments
Derivative assets:
Total assets measured at fair value on a recurring basis	0.0	0.0
Fair Value, Measurements, Recurring | Significant Other Unobservable Remaining Inputs (Level 3) | Long-term investments
Derivative assets:
Total assets measured at fair value on a recurring basis	0.0	0.0
Fair Value, Measurements, Recurring | Significant Other Unobservable Remaining Inputs (Level 3) | Prepaid expenses and other current assets
Derivative assets:
Total assets measured at fair value on a recurring basis	0.0	0.0
Fair Value, Measurements, Recurring | Significant Other Unobservable Remaining Inputs (Level 3) | Other long-term assets
Derivative assets:
Total assets measured at fair value on a recurring basis	61.1	55.7
Fair Value, Measurements, Recurring | Significant Other Unobservable Remaining Inputs (Level 3) | Other accrued liabilities
Liabilities:
Total liabilities measured at fair value on a recurring basis	0.0	0.0
Fair Value, Measurements, Recurring | Significant Other Unobservable Remaining Inputs (Level 3) | Other long-term liabilities
Liabilities:
Total liabilities measured at fair value on a recurring basis	0.0	0.0
Fair Value, Measurements, Recurring | Significant Other Unobservable Remaining Inputs (Level 3) | Foreign exchange contracts
Derivative assets:
Derivative assets:	0.0	0.0
Liabilities:
Derivative liabilities:	0.0	0.0
Fair Value, Measurements, Recurring | Significant Other Unobservable Remaining Inputs (Level 3) | Interest rate contracts
Derivative assets:
Derivative assets:	0.0	0.0
Fair Value, Measurements, Recurring | Significant Other Unobservable Remaining Inputs (Level 3) | Asset-backed securities
Available-for-sale debt securities:
Available-for-sale debt securities	0.0	0.0
Fair Value, Measurements, Recurring | Significant Other Unobservable Remaining Inputs (Level 3) | Certificates of deposit
Available-for-sale debt securities:
Available-for-sale debt securities	0.0	0.0
Fair Value, Measurements, Recurring | Significant Other Unobservable Remaining Inputs (Level 3) | Commercial paper
Available-for-sale debt securities:
Available-for-sale debt securities	0.0	0.0
Fair Value, Measurements, Recurring | Significant Other Unobservable Remaining Inputs (Level 3) | Corporate debt securities
Available-for-sale debt securities:
Available-for-sale debt securities	0.0	0.0
Fair Value, Measurements, Recurring | Significant Other Unobservable Remaining Inputs (Level 3) | Foreign government debt securities
Available-for-sale debt securities:
Available-for-sale debt securities	0.0	0.0
Fair Value, Measurements, Recurring | Significant Other Unobservable Remaining Inputs (Level 3) | Time deposits
Available-for-sale debt securities:
Available-for-sale debt securities	0.0	0.0
Fair Value, Measurements, Recurring | Significant Other Unobservable Remaining Inputs (Level 3) | U.S. government agency securities
Available-for-sale debt securities:
Available-for-sale debt securities	0.0	0.0
Fair Value, Measurements, Recurring | Significant Other Unobservable Remaining Inputs (Level 3) | U.S. government securities
Available-for-sale debt securities:
Available-for-sale debt securities	0.0	0.0
Fair Value, Measurements, Recurring | Significant Other Unobservable Remaining Inputs (Level 3) | Privately-held debt and redeemable preferred stock securities
Available-for-sale debt securities:
Available-for-sale debt securities	61.1	55.7
Fair Value, Measurements, Recurring | Significant Other Unobservable Remaining Inputs (Level 3) | Money market funds
Equity securities:
Equity securities	0.0	0.0
Fair Value, Measurements, Recurring | Significant Other Unobservable Remaining Inputs (Level 3) | Mutual funds
Equity securities:
Equity securities	0.0	0.0
Fair Value, Measurements, Recurring | Significant Other Unobservable Remaining Inputs (Level 3) | Publicly-traded equity securities
Equity securities:
Equity securities	$ 0.0	$ 0.0