Summary of Portfolio of Securities Held to Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013		Dec. 31, 2012
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 6,786,932	[1]	$ 4,505,831	[2]
Carrying Amount	6,777,715	[1]	4,484,262	[2]
Gross Unrealized Gain	96,089	[1]	235,700	[2]
Gross Unrealized Loss	246,548	[1]	14,002	[2]
Fair Value	6,627,256	[1]	4,705,960	[2]
Mortgage-Related Securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	3,943,372		3,155,217
Carrying Amount	3,943,372		3,155,217
Gross Unrealized Gain	76,193		192,624
Gross Unrealized Loss	60,956		5
Fair Value	3,958,609		3,347,836
Mortgage-Related Securities | GSE certificates
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	2,221,859		1,253,769
Carrying Amount	2,221,859		1,253,769
Gross Unrealized Gain	37,756		87,860
Gross Unrealized Loss	48,066		5
Fair Value	2,211,549		1,341,624
Mortgage-Related Securities | GSE CMOs
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	1,718,497		1,898,228
Carrying Amount	1,718,497		1,898,228
Gross Unrealized Gain	38,437		104,764
Gross Unrealized Loss	12,890
Fair Value	1,744,044		2,002,992
Mortgage-Related Securities | Other mortgage-related securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	3,016		3,220
Carrying Amount	3,016		3,220
Fair Value	3,016		3,220
Other Securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	2,843,560		1,350,614
Carrying Amount	2,834,343		1,329,045
Gross Unrealized Gain	19,896		43,076
Gross Unrealized Loss	185,592		13,997
Fair Value	2,668,647		1,358,124
Other Securities | GSE debentures
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	2,624,773		1,129,618
Carrying Amount	2,624,773		1,129,618
Gross Unrealized Gain	7,681		15,739
Gross Unrealized Loss	170,695
Fair Value	2,461,759		1,145,357
Other Securities | Corporate bonds
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	72,799		72,501
Carrying Amount	72,799		72,501
Gross Unrealized Gain	10,898		12,504
Fair Value	83,697		85,005
Other Securities | Municipal bonds
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	61,123		16,982
Carrying Amount	61,123		16,982
Gross Unrealized Gain	29		245
Gross Unrealized Loss	3,710
Fair Value	57,442		17,227
Other Securities | Capital trust notes
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	84,865		131,513
Carrying Amount	75,648		109,944
Gross Unrealized Gain	1,288		14,588
Gross Unrealized Loss	11,187		13,997
Fair Value	$ 65,749		$ 110,535

[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. At September 30, 2013, the non-credit portion of OTTI recorded in AOCL was $9.2 million (before taxes).

[2] At December 31, 2012, the non-credit portion of OTTI recorded in AOCL was $21.6 million (before taxes).