Summary of Portfolio of Securities Held to Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011		Dec. 31, 2010
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 3,837,591	[1]	$ 4,157,816	[2]
Carrying Amount	3,815,854	[1]	4,135,935	[2]
Gross Unrealized Gain	170,346	[1]	84,139	[2]
Gross Unrealized Loss	20,015	[1]	62,752	[2]
Fair Value	3,966,185	[1]	4,157,322	[2]
Mortgage-Related Securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	2,996,240		2,979,315
Carrying Amount	2,996,240		2,979,315
Gross Unrealized Gain	140,280		59,558
Gross Unrealized Loss			29,439
Fair Value	3,136,520		3,009,434
Mortgage-Related Securities | GSE certificates
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	660,945		208,993
Carrying Amount	660,945		208,993
Gross Unrealized Gain	47,064		12,206
Gross Unrealized Loss			1,094
Fair Value	708,009		220,105
Mortgage-Related Securities | GSE CMOs
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	2,331,916		2,763,545
Carrying Amount	2,331,916		2,763,545
Gross Unrealized Gain	93,216		47,352
Gross Unrealized Loss			28,345
Fair Value	2,425,132		2,782,552
Mortgage-Related Securities | Other mortgage-related securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	3,379		6,777
Carrying Amount	3,379		6,777
Fair Value	3,379		6,777
Other Securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	841,351		1,178,501
Carrying Amount	819,614		1,156,620
Gross Unrealized Gain	30,066		24,581
Gross Unrealized Loss	20,015		33,313
Fair Value	829,665		1,147,888
Other Securities | GSE debentures
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	633,258		924,663
Carrying Amount	633,258		924,663
Gross Unrealized Gain	14,878		4,524
Gross Unrealized Loss	146		10,592
Fair Value	647,990		918,595
Other Securities | Corporate bonds
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	54,759		86,483
Carrying Amount	54,759		86,483
Gross Unrealized Gain	2,826		8,647
Gross Unrealized Loss	12		13
Fair Value	57,573		95,117
Other Securities | Capital trust notes
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	153,334		167,355
Carrying Amount	131,597		145,474
Gross Unrealized Gain	12,362		11,410
Gross Unrealized Loss	19,857		22,708
Fair Value	$ 124,102		$ 134,176

[1] Held-to-maturity securities are reported at a carrying amount equal to amortized cost less the non-credit portion of OTTI recorded in AOCL. The non-credit portion of OTTI recorded in AOCL was $21.7 million (before taxes).

[2] The non-credit portion of OTTI recorded in AOCL was $21.9 million (before taxes).