Acquisitions - Net Assets Acquired Liabilities Assumed and Consideration Transferred at Fair Value (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Jun. 04, 2011
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items]
Business acquisition, purchase price allocation, core deposit intangibles amount		$ 189.4
Trade name [Member]
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items]
Business acquisition, purchase price allocation, core deposit intangibles amount		11.7
Amortization life, years	2 years 6 months
Trust Relationships [Member]
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items]
Business acquisition, purchase price allocation, core deposit intangibles amount		11.1
Credit Card Receivable [Member]
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items]
Business acquisition, purchase price allocation, core deposit intangibles amount		$ 11.3
Amortization life, years	15 years
Trust [Member]
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items]
Amortization life, years	12 years
Minimum [Member] | Core Deposit Intangibles [Member]
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items]
Amortization life, years	12 years
Maximum [Member] | Core Deposit Intangibles [Member]
Business Acquisition Actual Revenue And Pre Tax Income Loss [Line Items]
Amortization life, years	20 years