Effect of Change within Cash Flow from applying the Provision of the Revenue Accounting Standard (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cash flows from operating activities
Net income	$ 376.8	$ 345.9
Reconciliation of net income to net cash provided by operating activities:
Depreciation and amortization	49.1	32.5
Stock-based compensation expense	35.1	28.4
Deferred income taxes	(4.2)	185.0
Changes in assets and liabilities:
Accounts receivable	(29.9)	(61.9)
Other current assets	47.8	(128.3)
Other assets	(14.5)	(3.2)
Accounts payable and accrued liabilities	(224.2)	(988.6)
Deferred revenue	167.7	125.9
Unrecognized tax benefits and other non-current tax liabilities	(17.9)	0.9
Other liabilities	5.7	10.7
Net cash provided by (used in) operating activities	391.5	$ (512.4)
Under Previous Accounting Guidance [Member] | New Revenue Accounting Standard [Member]
Cash flows from operating activities
Net income	376.3
Reconciliation of net income to net cash provided by operating activities:
Depreciation and amortization	49.1
Stock-based compensation expense	35.1
Deferred income taxes	4.0
Changes in assets and liabilities:
Accounts receivable	(22.3)
Other current assets	36.1
Other assets	(10.6)
Accounts payable and accrued liabilities	(229.4)
Deferred revenue	164.5
Unrecognized tax benefits and other non-current tax liabilities	(17.9)
Other liabilities	6.6
Net cash provided by (used in) operating activities	391.5
Effect of Change [Member] | New Revenue Accounting Standard [Member]
Cash flows from operating activities
Net income	0.5
Reconciliation of net income to net cash provided by operating activities:
Deferred income taxes	(8.2)
Changes in assets and liabilities:
Accounts receivable	(7.6)
Other current assets	11.7
Other assets	(3.9)
Accounts payable and accrued liabilities	5.2
Deferred revenue	3.2
Other liabilities	$ (0.9)