Borrowings (Narrative) (Detail) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Federal Home Loan Bank, Advances [Line Items]
Pledged Financial Instruments, Not Separately Reported, Loans Receivable, for Federal Home Loan Bank Debt	$ 5,700.0	$ 5,200.0
Federal Home Loan Bank Advances [Member]
Federal Home Loan Bank, Advances [Line Items]
Federal Home Loan Bank, Advances, General Debt Obligations, Amount of Available, Unused Funds	1,200.0	700.0
Line of Credit [Member]
Federal Home Loan Bank, Advances [Line Items]
Federal Home Loan Bank, Advances, General Debt Obligations, Amount of Available, Unused Funds	$ 5.0	$ 5.0

Amount of advances or credit lines available from the Federal Home Loan Bank (FHLB).

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.13(3)(a))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22 (b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6479118&loc=d3e64650-112822

Name:	us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresAmountOfAvailableUnusedFunds
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant