Financial Instruments - Summary Of Cash And Available-For-Sale Securities (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Cash and Cash Equivalents	$ 1,167.6	$ 857.9
Total	4,678.2
Total assets measured at fair value, Amortized Cost	5,818.1	4,845.0
Gross Unrealized Gains	27.9	3.3
Gross Unrealized Losses	0.8	13.9
Fair Value	4,705.3
Total assets measured at fair value, Fair Value	5,845.2	4,834.4
Short-term Investments	2,054.1	2,205.2
Long-term Investments	2,623.5	1,771.3
Cash
Schedule of Available-for-sale Securities [Line Items]
Cash and Cash Equivalents	413.1	269.4
Fair Value	413.1	269.4
Level 1
Schedule of Available-for-sale Securities [Line Items]
Cash and Cash Equivalents	726.8	579.1
Total	2,662.6	2,046.9
Gross Unrealized Gains	9.7	1.7
Gross Unrealized Losses	0.4	5.3
Fair Value	2,671.9	2,043.3
Short-term Investments	890.8	897.8
Long-term Investments	1,054.3	566.4
Level 1 | Money market funds
Schedule of Available-for-sale Securities [Line Items]
Cash and Cash Equivalents	726.8	569.1
Fair Value	726.8	569.1
Short-term Investments	0.0	0.0
Long-term Investments	0.0	0.0
Level 1 | U.S. treasuries
Schedule of Available-for-sale Securities [Line Items]
Cash and Cash Equivalents	0.0	10.0
Total	1,935.8	1,477.8
Gross Unrealized Gains	9.7	1.7
Gross Unrealized Losses	0.4	5.3
Fair Value	1,945.1	1,474.2
Short-term Investments	890.8	897.8
Long-term Investments	1,054.3	566.4
Level 2
Schedule of Available-for-sale Securities [Line Items]
Cash and Cash Equivalents	27.7	9.4
Total	2,742.4	2,528.7
Gross Unrealized Gains	18.2	1.6
Gross Unrealized Losses	0.4	8.6
Fair Value	2,760.2	2,521.7
Short-term Investments	1,163.3	1,307.4
Long-term Investments	1,569.2	1,204.9
Level 2 | Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Cash and Cash Equivalents	25.5	1.4
Total	165.1	110.7
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses	0.0	0.0
Fair Value	165.1	110.7
Short-term Investments	139.6	109.3
Long-term Investments	0.0	0.0
Level 2 | Corporate securities
Schedule of Available-for-sale Securities [Line Items]
Cash and Cash Equivalents	0.0	8.0
Total	2,096.1	1,607.8
Gross Unrealized Gains	16.8	1.3
Gross Unrealized Losses	0.2	4.8
Fair Value	2,112.7	1,604.3
Short-term Investments	798.5	724.5
Long-term Investments	1,314.2	871.8
Level 2 | U.S. government agencies
Schedule of Available-for-sale Securities [Line Items]
Cash and Cash Equivalents	0.0	0.0
Total	418.3	791.8
Gross Unrealized Gains	1.1	0.3
Gross Unrealized Losses	0.2	3.8
Fair Value	419.2	788.3
Short-term Investments	209.6	468.9
Long-term Investments	209.6	319.4
Level 2 | Non-U.S. government securities
Schedule of Available-for-sale Securities [Line Items]
Cash and Cash Equivalents	0.0
Total	4.5
Gross Unrealized Gains	0.0
Gross Unrealized Losses	0.0
Fair Value	4.5
Short-term Investments	4.5
Long-term Investments	0.0
Level 2 | Municipal securities
Schedule of Available-for-sale Securities [Line Items]
Cash and Cash Equivalents	2.2	0.0
Total	58.4	18.4
Gross Unrealized Gains	0.3	0.0
Gross Unrealized Losses	0.0	0.0
Fair Value	58.7	18.4
Short-term Investments	11.1	4.7
Long-term Investments	$ 45.4	$ 13.7