Cash Equivalent and Investments (Detail) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015	Dec. 31, 2014
Schedule Of Available For Sale Securities [Line Items]
Fair value	$ 32.9	$ 31.9
Cash and cash equivalents	1,674.3	1,757.4	$ 1,538.6	$ 1,219.5
Short-term investments	352.5	474.8
Money Market [Member]
Schedule Of Available For Sale Securities [Line Items]
Cost	55.5	188.3
Gross unrealized gain
Fair value	55.5	188.3
Cash and cash equivalents	55.5	188.3
Short-term investments
Other assets
Certificates Of Deposit [Member]
Schedule Of Available For Sale Securities [Line Items]
Cost	913.2	1,307.3
Gross unrealized gain
Fair value	913.2	1,307.3
Cash and cash equivalents	533.7	809.4
Short-term investments	352.5	474.8
Other assets	27.0	23.1
Fixed Maturity and Mutual Funds [Member]
Schedule Of Available For Sale Securities [Line Items]
Cost	28.5	28.7
Gross unrealized gain	4.4	3.2
Fair value	32.9	31.9
Cash and cash equivalents
Short-term investments
Other assets	$ 32.9	$ 31.9