Derivative Financial Instruments (Counterparty Credit Risk Narrative) (Detail) $ in Millions	Jun. 30, 2017 USD ($)
Derivative [Line Items]
Derivative, Collateral, Right to Reclaim Cash	$ 28.1
Derivative Asset, Collateral, Obligation to Return Cash, Offset	30.7
Derivative Liability, Collateral, Right to Reclaim Cash, Offset	(2.6)
Credit Derivative, Maximum Exposure, Undiscounted	38.5
Market Approach Valuation Technique [Member]
Derivative [Line Items]
Credit Derivative, Maximum Exposure, Undiscounted	$ 27.4