Cash Equivalent and Investments (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Money Market [Member]
Schedule of Available-for-sale Securities [Line Item]
Cost	$ 188.3	$ 149.7
Fair Value	188.3	149.7
Cash and Cash Equivalents	188.3	149.7
Certificates of Deposit [Member]
Schedule of Available-for-sale Securities [Line Item]
Cost	1,307.3	842.5
Fair Value	1,307.3	842.5
Cash and Cash Equivalents	809.4	380.1
Short Term Investments	474.8	458.1
Other Assets	23.1	4.3
Fixed Maturity and Mutual Funds [Member]
Schedule of Available-for-sale Securities [Line Item]
Cost	28.7	47.1
Gross Unrealized Gain	3.2	0.9
Fair Value	31.9	48.0
Other Assets	$ 31.9	$ 48.0