Commitments, Contingencies and Guarantees - Additional Information (Detail) $ in Millions	9 Months Ended
	Sep. 30, 2017 USD ($) attorney_general_office
Commitments and Contingencies Disclosure [Abstract]
Contractual obligation	$ 1,900.0
Other liabilities reserve	$ 1.6
Loss contingency, loss emergence period	1 year
Number of attorneys general | attorney_general_office	2