Securities (Details 3) (USD $) In Thousands	Sep. 30, 2011
Held to Maturity:
Due in one year or less, estimated fair market value	$ 2
Due after one year through five years, estimated fair market value	1,679
Due after five years through ten years, estimated fair market value	9,840
Due after ten years, estimated fair market value	6,446,037
Total held to maturity, estimated fair market value	6,457,558
Available for Sale:
Due after ten years, estimated fair market value	9,905,741
Total available for sale, estimated fair market value	9,905,741
Mortgage-backed securities [Member]
Available for Sale:
Due after ten years, amortized cost	9,748,718
Total available for sale, amortized cost	9,748,718
Mortgage-backed securities [Member]
Held to Maturity:
Due in one year or less, amortized cost	2
Due after one year through five years, amortized cost	1,546
Due after five years through ten years, amortized cost	9,231
Due after ten years, amortized cost	4,522,778
Total held to maturity, amortized cost	4,533,557
Investment Securities [Member]
Available for Sale:
Due after ten years, amortized cost	0
Total available for sale, amortized cost	0
Investment Securities [Member]
Held to Maturity:
Due in one year or less, amortized cost	0
Due after one year through five years, amortized cost	0
Due after five years through ten years, amortized cost	0
Due after ten years, amortized cost	1,638,954
Total held to maturity, amortized cost	$ 1,638,954

Estimated fair value of held to maturities securities.

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name FASB Staff Position (FSP)

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-Paragraph 7

-Footnote 2

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 20

-Subparagraph d

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This item represents the fair value of debt securities which are expected to mature after ten years from the balance sheet date which are categorized neither as held-to-maturity nor trading securities.

+ References

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-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 20

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This item represents the total of all debt securities grouped by maturity dates, at fair value, which are categorized neither as held-to-maturity nor trading securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 20

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This item represents the fair value of debt securities which are expected to mature after five years and through ten years from the balance sheet date and which are categorized as held-to-maturity.

+ References

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-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 20

-Subparagraph c

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+ References

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+ References

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-Name Statement of Financial Accounting Standard (FAS)

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+ References

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-Name Statement of Financial Accounting Standard (FAS)

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This item represents the fair value of debt securities which are expected to mature within one year of the balance sheet date and which are categorized as held-to-maturity.

+ References

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-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

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This item represents debt securities, at cost, net of adjustments made for accretion, amortization, other-than-temporary impairments, and hedging, if any, which are expected to mature within one year of the balance sheet date and which are categorized as held-to-maturity.

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