Summary of Carrying Amount and Estimated Fair Value of Held-to-Maturity Debt Securities and Amortized Cost and Estimated Fair Value of Available-for-Sale Debt Securities by Contractual Maturity (Detail) (USD $)	Sep. 30, 2011		Dec. 31, 2010
Held-to-Maturity Securities:
Total debt securities held to maturity	$ 4,648,551,000	[1]	$ 4,135,935,000	[2]
Held-to-Maturity Securities:
Due within one year	8,761,000
Due from one to five years	24,798,000
Due from five to ten years	2,256,407,000
Due after ten years	2,504,407,000
Fair Value	4,794,373,000	[1]	4,157,322,000	[2]
Available-for-Sale Securities:
Due within one year	126,000
Due from one to five years	3,084,000
Due from five to ten years	365,628,000
Due after ten years	92,273,000
Total debt securities available for sale	461,111,000	[3]
Mortgage-Related Securities
Held-to-Maturity Securities:
Due from five to ten years	868,209,000
Due after ten years	2,267,137,000
Total debt securities held to maturity	3,135,346,000		2,979,315,000
Available-for-Sale Securities:
Due from one to five years	2,531,000
Due from five to ten years	64,734,000
Due after ten years	60,472,000
Total debt securities available for sale	127,737,000	[3]
Held-to-Maturity Securities Average Yield
Due from five to ten years, Average Yield	3.76%
Due after ten years, Average Yield	3.74%
Total debt securities held to maturity, Average Yield	3.75%
Available-for-Sale Securities Average Yield
Due from one to five years, Average Yield	6.91%
Due from five to ten years, Average Yield	4.11%
Due after ten years, Average Yield	4.74%
Total debt securities available for sale, Average Yield	4.46%	[3]
Held-to-Maturity Securities:
Fair Value	3,276,303,000		3,009,434,000
U.S. Treasury and GSE Obligations
Held-to-Maturity Securities:
Due from five to ten years	1,298,132,000
Total debt securities held to maturity	1,298,132,000
Available-for-Sale Securities:
Due from five to ten years	295,160,000
Due after ten years	594,000
Total debt securities available for sale	295,754,000	[3]
Held-to-Maturity Securities Average Yield
Due from five to ten years, Average Yield	3.92%
Total debt securities held to maturity, Average Yield	3.92%
Available-for-Sale Securities Average Yield
Due from five to ten years, Average Yield	3.77%
Due after ten years, Average Yield	2.75%
Total debt securities available for sale, Average Yield	3.76%	[3]
State, county, and municipal
Available-for-Sale Securities:
Due within one year	125,000
Due from one to five years	489,000
Due from five to ten years	696,000
Total debt securities available for sale	1,310,000	[3]
Available-for-Sale Securities Average Yield
Due within one year, Average Yield	5.39%	[4]
Due from one to five years, Average Yield	6.01%	[4]
Due from five to ten years, Average Yield	6.52%	[4]
Total debt securities available for sale, Average Yield	6.23%	[3],[4]
Other Debt Securities
Held-to-Maturity Securities:
Due within one year	8,750,000	[5]
Due from one to five years	23,986,000	[5]
Due from five to ten years	20,023,000	[5]
Due after ten years	162,314,000	[5]
Total debt securities held to maturity	215,073,000	[5]
Available-for-Sale Securities:
Due after ten years	36,754,000	[5]
Total debt securities available for sale	$ 36,754,000	[3],[5]
Held-to-Maturity Securities Average Yield
Due within one year, Average Yield	7.79%
Due from one to five years, Average Yield	5.80%
Due from five to ten years, Average Yield	5.98%
Due after ten years, Average Yield	7.17%
Total debt securities held to maturity, Average Yield	6.94%
Available-for-Sale Securities Average Yield
Due after ten years, Average Yield	4.62%
Total debt securities available for sale, Average Yield	4.62%	[3]

[1] Held-to-maturity securities are reported at a carrying amount equal to amortized cost less the non-credit portion of OTTI recorded in accumulated other comprehensive loss, net of tax ("AOCL"). The non-credit portion of OTTI was $21.8 million (before taxes).

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

[3] As equity securities have no contractual maturity, they have been excluded from this table.

[4] Not presented on a tax-equivalent basis.

[5] Includes corporate bonds and capital trust notes. Included in capital trust notes are $15.5 million and $629,000 of pooled trust preferred securities available for sale and held to maturity, respectively, all of which are due after ten years. The remaining capital trust notes consist of single-issue trust preferred securities.