Acquisitions - Additional Information (Detail) (USD $)	Jun. 30, 2013	Dec. 31, 2012	Aug. 27, 2012
Business Acquisition [Line Items]
Purchase consideration per common share			$ 0.08403
Total consideration to be paid	$ 4,700,000,000
Assets	83,229,005,000	83,008,803,000
Investment securities	5,210,526,000	6,074,361,000
Liabilities	72,512,675,000	72,806,210,000
Deposits	65,661,470,000	65,611,253,000
Hudson City [Member]
Business Acquisition [Line Items]
Assets	39,700,000,000
Loans	25,300,000,000
Investment securities	10,600,000,000
Liabilities	35,000,000,000
Deposits	$ 22,600,000,000
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%