Acquisitions - Additional Information (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012	Aug. 27, 2012
Business Acquisition [Line Items]
Purchase consideration per common share			0.08403
Total consideration to be paid	$ 4,800,000,000
Assets	84,427,485,000	83,008,803,000
Investment securities	8,309,773,000	6,074,361,000
Liabilities	73,411,283,000	72,806,210,000
Deposits	66,552,141,000	65,611,253,000
Hudson City [Member]
Business Acquisition [Line Items]
Assets	39,200,000,000
Loans	24,700,000,000
Investment securities	10,000,000,000
Liabilities	34,500,000,000
Deposits	$ 22,100,000,000
Cash [Member]
Business Acquisition [Line Items]
Percentage of total consideration			40.00%
Common stock [Member]
Business Acquisition [Line Items]
Percentage of total consideration			60.00%