Commitments, Contingencies and Guarantees - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) attorney_general attorney_general_office
Loss Contingencies [Line Items]
Contractual obligation	$ 1,800.0
Other liabilities reserve	$ 1.9
Loss emergence period	1 year
Number of state attorneys general | attorney_general_office	2
Washington and Pennsylvania
Loss Contingencies [Line Items]
Number of state attorneys general | attorney_general	2