Fair Value Measurements (Details) - Narrative (USD $)	6 Months Ended	12 Months Ended
Jun. 30, 2012	Dec. 31, 2011
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available for sale fixed income securities, Fair Value	$ 26,242,802,000	$ 26,190,025,000
Available for sale fixed income securities, Amortized Cost	25,442,779,000	25,771,715,000
Fair value of securities - AFS	26,999,238,000	27,017,285,000
Available-for-sale Securities, Amortized Cost Basis	26,223,815,000	26,611,778,000
Derivative, Collateral, Obligation to Return Cash	124,700,000	77,100,000
Other investments - structured transactions	314,000,000	323,700,000
Spread on US Treasury rate for determining discount rate for fair value of deposit liabilities	1.397%	1.618%
Corporate [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available for sale fixed income securities, Fair Value	9,721,153,000	10,108,622,000
Available for sale fixed income securities, Amortized Cost	9,297,657,000	9,866,677,000
Medium-term Notes [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available for sale fixed income securities, Fair Value	186,100,000	266,000,000
Available for sale fixed income securities, Amortized Cost	199,100,000	297,700,000
Other Asset Backed Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available for sale fixed income securities, Fair Value	1,407,738,000	1,340,249,000
Available for sale fixed income securities, Amortized Cost	1,392,065,000	1,341,309,000
Covered Bonds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available for sale fixed income securities, Fair Value	500,500,000	353,900,000
Available for sale fixed income securities, Amortized Cost	478,100,000	345,400,000
Fixed Income Funds Member
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of securities - AFS	95,800,000	91,600,000
Available-for-sale Securities, Amortized Cost Basis	$ 100,000,000	$ 100,000,000

For an unclassified balance sheet, this item represents investments in debt and equity securities which are categorized neither as held-to-maturity nor trading.

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+ Details

- Definition

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References+ Details

- Definition

This item represents the total of all debt securities grouped by maturity dates, at cost, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments, as defined), and fair value hedge accounting adjustments, if any, which are classified neither as held-to-maturity nor trading securities.

+ References+ Details

- Definition

For an unclassified balance sheet, total of debt securities categorized neither as held-to-maturity nor trading.

+ References

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

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+ Details