Condensed Consolidated Statements Of Cash Flows - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021
Cash flows from operating activities:
Net income	$ 324.8	$ 298.1
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation of property and equipment	23.8	23.6
Stock-based compensation	27.9	26.6
Other Noncash Income (Expense)	(1.5)	(4.4)
Changes in operating assets and liabilities
Other assets	1.1	(18.6)
Accounts payable and accrued liabilities	(41.9)	(36.8)
Deferred revenues	28.2	50.0
Deferred Income Taxes	(13.4)	(6.5)
Net cash provided by operating activities	352.0	340.8
Net Cash Provided by (Used in) Investing Activities [Abstract]
Proceeds from maturities and sales of marketable securities	1,057.4	1,483.0
Purchases of marketable securities	(465.2)	(1,623.6)
Purchases of property and equipment	(12.8)	(24.3)
Net cash used in investing activities	579.4	(164.9)
Cash flows from financing activities:
Proceeds from employee stock purchase plans	8.2	8.1
Repayments of Debt, Maturing in More than Three Months	0.0	(750.0)
Payments for Repurchase of Common Stock	556.1	361.2
Proceeds from Debt, Net of Issuance Costs	0.0	742.3
Net cash used in financing activities	(547.9)	(360.8)
Effect of Exchange Rate on Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	(0.7)	(0.3)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect	382.8	(185.2)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, beginning of period	228.8	410.6
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, end of period	611.6	225.4
Supplemental cash flow disclosures:
Cash paid for interest	36.4	48.7
Cash paid for income taxes, net of refunds received	$ 113.3	$ 99.0