LOAN PORTFOLIO-Corporation's Aging of Purchased Credit Impaired Loans (Parenthetical) (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Residential Mortgage [Member]
Accounts Notes And Loans Receivable [Line Items]
Financing Receivable Recorded Investment 30 To 59 Days Past Due Mortgage	$ 142.8	$ 162.9
Residential Mortgage [Member] | Certain Loans Acquired In Transfer Not Accounted For As Debt Securities [Member]
Accounts Notes And Loans Receivable [Line Items]
Financing Receivable Recorded Investment 30 To 59 Days Past Due Mortgage	22.3	23.6
Commercial Mortgage [Member]
Accounts Notes And Loans Receivable [Line Items]
Financing Receivable Recorded Investment 30 To 59 Days Past Due Mortgage	4.6	$ 38.6
Commercial Mortgage [Member] | Certain Loans Acquired In Transfer Not Accounted For As Debt Securities [Member]
Accounts Notes And Loans Receivable [Line Items]
Financing Receivable Recorded Investment 30 To 59 Days Past Due Mortgage	$ 0.1