Securities (Details 1) (USD $) In Thousands	6 Months Ended	12 Months Ended
Jun. 30, 2011	Dec. 31, 2010
Amortized cost and estimated fair market value of securities held to maturity
Estimated Fair Market Value	$ 3,601,261	$ 3,867,488
Mortgage-backed securities [Member]
Amortized cost and estimated fair market value of securities held to maturity
Amortized Cost	4,896,216	5,914,372
Gross Unrealized Gains	278,898	285,167
Gross Unrealized Losses	(3)	(32)
Estimated Fair Market Value	5,175,111	6,199,507
Mortgage-backed securities [Member] \| GNMA pass-through certificates [Member]
Amortized cost and estimated fair market value of securities held to maturity
Amortized Cost	93,571	98,887
Gross Unrealized Gains	3,375	2,802
Gross Unrealized Losses	0
Estimated Fair Market Value	96,946	101,689
Mortgage-backed securities [Member] \| FNMA pass-through certificates [Member]
Amortized cost and estimated fair market value of securities held to maturity
Amortized Cost	1,379,845	1,622,994
Gross Unrealized Gains	85,863	87,271
Gross Unrealized Losses	(3)
Estimated Fair Market Value	1,465,705	1,710,265
Mortgage-backed securities [Member] \| FHLMC pass-through certificates [Member]
Amortized cost and estimated fair market value of securities held to maturity
Amortized Cost	2,482,825	2,943,565
Gross Unrealized Gains	142,010	148,248
Gross Unrealized Losses	0
Estimated Fair Market Value	2,624,835	3,091,813
Mortgage-backed securities [Member] \| FHLMC and FNMA - REMICs [Member]
Amortized cost and estimated fair market value of securities held to maturity
Amortized Cost	939,975	1,248,926
Gross Unrealized Gains	47,650	46,846
Gross Unrealized Losses	0	(32)
Estimated Fair Market Value	987,625	1,295,740
Investment Securities [Member]
Amortized cost and estimated fair market value of securities held to maturity
Amortized Cost	3,638,950	3,939,006
Gross Unrealized Gains	3,913	3,698
Gross Unrealized Losses	(41,602)	(75,216)
Estimated Fair Market Value	3,601,261	3,867,488
Investment Securities [Member] \| United States government-sponsored enterprise debt [Member]
Amortized cost and estimated fair market value of securities held to maturity
Amortized Cost	3,638,950	3,939,006
Gross Unrealized Gains	3,913	3,698
Gross Unrealized Losses	(41,602)	(75,216)
Estimated Fair Market Value	$ 3,601,261	$ 3,867,488

Held to Maturity Securities.

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- Definition

This item represents the total of all debt securities grouped by maturity dates, at fair value, which are categorized as held-to-maturity.

+ Details

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- Definition

This item represents the total of all debt securities grouped by maturity dates, at cost, net of adjustments made for accretion, amortization, other-than-temporary impairments, and hedging, if any, which are classified as held-to-maturity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 115
-Paragraph 20

+ Details

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- Definition

As of the balance sheet date, the excess of fair value over carrying value (amortized cost) of a debt security categorized as held-to-maturity, exclusive of dividend or interest income recognized but not yet received and exclusive of any write-downs for other-than-temporary impairment. Such item represents the gross unrecognized holding gain.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 115
-Paragraph 19

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 115
-Paragraph 137

+ Details

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- Definition

As of the balance sheet date, the excess of carrying value (amortized cost) over fair value of a debt security categorized as held-to-maturity, exclusive of dividend or interest income recognized but not yet received and exclusive of any write-downs for other-than-temporary impairment. Such item represents the gross unrecognized holding loss.

+ References

+ Details

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