Fair Value Measurements (Details) (USD $) In Thousands	Jun. 30, 2011	Dec. 31, 2010
Carrying value of assets measured at fair value on a recurring basis
Total available for sale debt securities	$ 10,484,264	$ 18,203,184
Total available for sale equity securities	7,221	7,148
Total available for sale securities	10,491,485	18,210,332
Mortgage-backed securities [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Carrying value of assets measured at fair value on a recurring basis
Total available for sale debt securities	0	0
United States government-sponsored enterprise securities [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Carrying value of assets measured at fair value on a recurring basis
Total available for sale debt securities		0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Carrying value of assets measured at fair value on a recurring basis
Total available for sale debt securities	0	0
Total available for sale equity securities	7,221	7,148
Total available for sale securities	7,221	7,148
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Financial Services Industry [Member]
Carrying value of assets measured at fair value on a recurring basis
Total available for sale equity securities	7,221	7,148
Mortgage-backed securities [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Carrying value of assets measured at fair value on a recurring basis
Total available for sale debt securities	10,484,264	18,120,537
United States government-sponsored enterprise securities [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Carrying value of assets measured at fair value on a recurring basis
Total available for sale debt securities		82,647
Significant Other Observable Inputs (Level 2) [Member]
Carrying value of assets measured at fair value on a recurring basis
Total available for sale debt securities	10,484,264	18,203,184
Total available for sale equity securities	0	0
Total available for sale securities	10,484,264	18,203,184
Significant Other Observable Inputs (Level 2) [Member] \| Financial Services Industry [Member]
Carrying value of assets measured at fair value on a recurring basis
Total available for sale equity securities	0	0
Mortgage-backed securities [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Carrying value of assets measured at fair value on a recurring basis
Total available for sale debt securities	0	0
United States government-sponsored enterprise securities [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Carrying value of assets measured at fair value on a recurring basis
Total available for sale debt securities		0
Significant Unobservable Inputs (Level 3) [Member]
Carrying value of assets measured at fair value on a recurring basis
Total available for sale debt securities	0	0
Total available for sale equity securities	0	0
Total available for sale securities	0	0
Significant Unobservable Inputs (Level 3) [Member] \| Financial Services Industry [Member]
Carrying value of assets measured at fair value on a recurring basis
Total available for sale equity securities	0	0
Mortgage-backed securities [Member]
Carrying value of assets measured at fair value on a recurring basis
Total available for sale debt securities	10,484,264	18,120,537
United States government-sponsored enterprise securities [Member]
Carrying value of assets measured at fair value on a recurring basis
Total available for sale debt securities		82,647
Financial Services Industry [Member]
Carrying value of assets measured at fair value on a recurring basis
Total available for sale equity securities	$ 7,221	$ 7,148

For an unclassified balance sheet, this item represents investments in debt and equity securities which are categorized neither as held-to-maturity nor trading. Such securities are reported at fair value, with unrealized gains and losses excluded from earnings and reported in a separate component of shareholders' equity (other comprehensive income), unless the Available-for-sale Security is designated as a hedge or is determined to have had an other than temporary decline in fair value below its amortized cost basis. All or a portion of the unrealized holding gain or loss of an Available-for-sale Security that is designated as being hedged in a fair value hedge shall be recognized in earnings during the period of the hedge, as should other than temporary declines in fair value below costs basis.

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For an unclassified balance sheet, total of debt securities categorized neither as held-to-maturity nor trading. Such securities are reported at fair value; unrealized gains and losses of such securities are excluded from earnings and included in other comprehensive income, a separate component of shareholders' equity, unless the Available-for-sale Security is designated as a hedge or is determined to have had an other than temporary decline in fair value below its amortized cost basis. All or a portion of the unrealized holding gain or loss of an Available-for-sale Security that is designated as being hedged in a fair value hedge shall be recognized in earnings during the period of the hedge, as should other than temporary declines in fair value below costs basis.

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- Definition

For an unclassified balance sheet, this item represents equity securities categorized neither as held-to-maturity nor trading. Equity securities represent ownership interests or the right to acquire ownership interests in corporations and other legal entities which ownership interest is represented by shares of common or preferred stock (which is not mandatorily redeemable or redeemable at the option of the holder), convertible securities, stock rights, or stock warrants. Unrealized gains and losses related to Available-for-sale Securities are excluded from earnings and reported in a separate component of shareholders' equity (other comprehensive income), unless the Available-for-sale Security is designated as a hedge or is determined to have had an other than temporary decline in fair value below its amortized cost basis. All or a portion of the unrealized holding gain or loss of an Available-for-sale Security that is designated as being hedged in a fair value hedge shall be recognized in earnings during the period of the hedge, as should other than temporary declines in fair value below costs basis.

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