Effect of Change within Cash Flow from applying the Provision of the Revenue Accounting Standard (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Cash flows from operating activities
Net income	$ 377.9	$ 313.6	$ 754.7	$ 659.5
Reconciliation of net income to net cash provided by operating activities:
Depreciation and amortization	48.4	32.9	97.5	65.4
Stock-based compensation expense	34.4	$ 28.7	69.5	57.1
Deferred income taxes			(12.1)	193.5
Changes in assets and liabilities:
Accounts receivable			17.8	(16.5)
Other current assets			(10.2)	(91.0)
Other assets			(14.3)	8.9
Accounts payable and accrued liabilities			(163.2)	(877.4)
Deferred revenue			55.3	43.9
Unrecognized tax benefits and other non-current tax liabilities			(33.6)	8.4
Other liabilities			15.9	8.5
Net cash provided by (used in) operating activities			777.3	$ (40.6)
Under Previous Accounting Guidance [Member] | New Revenue Accounting Standard [Member]
Cash flows from operating activities
Net income	372.1		748.4
Reconciliation of net income to net cash provided by operating activities:
Depreciation and amortization	48.4		97.5
Stock-based compensation expense			69.5
Deferred income taxes			2.0
Changes in assets and liabilities:
Accounts receivable			15.2
Other current assets			(20.4)
Other assets			(21.0)
Accounts payable and accrued liabilities			(158.1)
Deferred revenue			55.9
Unrecognized tax benefits and other non-current tax liabilities			(33.6)
Other liabilities			21.9
Net cash provided by (used in) operating activities			777.3
Effect of Change [Member] | New Revenue Accounting Standard [Member]
Cash flows from operating activities
Net income	$ 5.8		6.3
Reconciliation of net income to net cash provided by operating activities:
Deferred income taxes			(14.1)
Changes in assets and liabilities:
Accounts receivable			2.6
Other current assets			10.2
Other assets			6.7
Accounts payable and accrued liabilities			(5.1)
Deferred revenue			(0.6)
Other liabilities			$ (6.0)