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Investments (Investment Securities Whose Book Value Exceeded Market Value By More Than 5%) (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012 Security
Five Percent To Less Than Sixteen Percent [Member]
Schedule of Investments [Line Items]
Number of Securities	35
Book Value	$ 279
Fair Value	250
Percentage Book Value Exceeded Market Value, Minimum	5.00%
Percentage Book Value Exceeded Market Value, Maximum	16.00%
Sixteen Percent To Less Than Twenty Six Percent [Member]
Schedule of Investments [Line Items]
Number of Securities	23
Book Value	791
Fair Value	621
Percentage Book Value Exceeded Market Value, Minimum	16.00%
Percentage Book Value Exceeded Market Value, Maximum	26.00%
26% To 50% [Member]
Schedule of Investments [Line Items]
Number of Securities	34
Book Value	120
Fair Value	75
Percentage Book Value Exceeded Market Value, Minimum	26.00%
Percentage Book Value Exceeded Market Value, Maximum	50.00%
Greater Than 50% [Member]
Schedule of Investments [Line Items]
Number of Securities	26
Book Value	87
Fair Value	18
Percentage Book Value Exceeded Market Value, Maximum	50.00%
Greater Than 5% [Member]
Schedule of Investments [Line Items]
Number of Securities	118
Book Value	1,277
Fair Value	$ 964

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- Definition

Disclosure regarding factors used to determine that the impairment of securities not categorized as trading securities (hence equal to available for sale and held to maturity securities) where cost exceeds fair value. This item contains disclosure of the number of investment positions in the investments determined to be temporarily impaired.

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- Definition

Investments Securities In Unrealized Loss Position For Continuous Twelve Month Period or Longer At Fair Value

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- Definition

Investments Securities In Unrealized Loss Position For Continuous Twelve Month Period or Longer Book Value

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- Definition

Percentage Book Value Exceeded Market Value, Maximum

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- Definition

Percentage Book Value Exceeded Market Value, Minimum

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