Employee Incentive and Retirement Plans - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option granted to purchase of common stock (shares)			1,164,929
Options granted, weighted average exercise price ($ per share)			$ 20.00
Options exercised (shares)			5,407,540	5,638,830
Total intrinsic values of options exercised			$ 75.3	$ 40.4
Total fair value of shares vested			$ 26.0	14.7
Expense related to accelerated vesting of stock options				3.0
Purchased by employees (number of shares)			211,256
Internally Developed Software
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense, capitalized amount	$ 1.3	$ 0.6	$ 3.1	$ 1.2
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option granted to purchase of common stock (shares)				18,511,572
Options granted, weighted average exercise price ($ per share)				$ 5.91
Common stock, weighted average grant date fair value per share ($ per share)			$ 9.80	$ 4.37
Options granted, total estimated fair value			$ 11.4	$ 81.0
Unrecognized compensation cost	100.8		$ 100.8
Unrecognized compensation cost expected period for recognition			2 years 7 months 6 days
RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost expected period for recognition			3 years 7 months 6 days
RSUs granted (shares)			3,518,967
Aggregate fair value			$ 58.4
Unrecognized compensation cost	$ 54.3		$ 54.3
Available for ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Purchase period			6 months
Purchase price of common stock			85.00%
Total common stock authorized and reserved for future issuance (shares)	2,788,744		2,788,744
Requisite service period			6 months