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Derivative Instruments (Narrative) (Details) (USD $)
Share data in Millions, except Per Share data, unless otherwise specified |
3 Months Ended | 6 Months Ended | 0 Months Ended | 3 Months Ended | 6 Months Ended | 0 Months Ended | 6 Months Ended | 6 Months Ended | |||||||||||||||||
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Jun. 30, 2012
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Jun. 30, 2011
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Jun. 30, 2012
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Jun. 30, 2011
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Jan. 20, 2011
Platinum [Member]
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Jun. 30, 2012
Interest Rate Contract [Member]
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Dec. 31, 2011
Interest Rate Contract [Member]
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Jun. 30, 2012
Foreign Currency Forward Contracts, Underwriting and Non-investment Operations [Member]
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Dec. 31, 2011
Foreign Currency Forward Contracts, Underwriting and Non-investment Operations [Member]
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Jun. 30, 2012
Foreign Currency Forward Contracts, Investment Operations [Member]
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Dec. 31, 2011
Foreign Currency Forward Contracts, Investment Operations [Member]
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Jun. 30, 2012
Foreign Currency Forward Contracts, Energy And Risk Operations [Member]
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Dec. 31, 2011
Foreign Currency Forward Contracts, Energy And Risk Operations [Member]
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Jun. 30, 2012
Credit Risk Contract [Member]
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Dec. 31, 2011
Credit Risk Contract [Member]
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Jun. 30, 2012
Energy And Weather Contracts [Member]
Other (Loss) Income [Member]
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Jun. 30, 2011
Energy And Weather Contracts [Member]
Other (Loss) Income [Member]
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Jun. 30, 2012
Energy And Weather Contracts [Member]
Other (Loss) Income [Member]
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Jun. 30, 2011
Energy And Weather Contracts [Member]
Other (Loss) Income [Member]
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Jan. 20, 2011
Platinum Warrant [Member]
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Jan. 20, 2011
Platinum Warrant [Member]
Other (Loss) Income [Member]
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Jun. 30, 2012
Platinum Warrant [Member]
Other (Loss) Income [Member]
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Jun. 30, 2011
Platinum Warrant [Member]
Other (Loss) Income [Member]
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Jun. 30, 2012
Renaissance Trading [Member]
Energy And Weather Contracts [Member]
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Jun. 30, 2012
Value at Risk Valuation Technique [Member]
Energy And Weather Contracts [Member]
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| Derivative [Line Items] | |||||||||||||||||||||||||
| Notional amount of interest rate derivative purchase contracts | $ 360,200,000 | $ 3,200,000,000 | |||||||||||||||||||||||
| Notional amount of interest rate derivative sale contracts | 303,700,000 | 285,700,000 | |||||||||||||||||||||||
| Notional amount of foreign currency derivative purchase contracts | 179,700,000 | 160,500,000 | 198,300,000 | 48,100,000 | 0 | 7,800,000 | |||||||||||||||||||
| Notional amount of foreign currency derivative sale contracts | 503,400,000 | 700,800,000 | 284,600,000 | 211,600,000 | 16,700,000 | 12,700,000 | |||||||||||||||||||
| Notional amount of credit risk derivative purchase contracts | 15,000,000 | 15,000,000 | |||||||||||||||||||||||
| Notional amount of credit risk derivative sale contracts | 24,400,000 | 38,100,000 | |||||||||||||||||||||||
| Value at risk, likelihood of potential loss being within estimate | 99.00% | ||||||||||||||||||||||||
| Value at risk, likelihood of potential loss exceeding estimate | 1.00% | ||||||||||||||||||||||||
| Value at risk of portfolio at period end | 42,000,000 | ||||||||||||||||||||||||
| Value at risk of portfolio during the period, average | 26,400,000 | ||||||||||||||||||||||||
| Value at risk of portfolio during the period, minimum | 13,000,000 | ||||||||||||||||||||||||
| Value at risk of portfolio during the period, maximum | 49,300,000 | ||||||||||||||||||||||||
| Guarantees | 354,300,000 | ||||||||||||||||||||||||
| Platinum Warrant, Shares | 2.5 | ||||||||||||||||||||||||
| Platinum Warrant, in dollars per share | $ 27 | ||||||||||||||||||||||||
| Aggregate proceeds from sale of Platinum Warrant | 47,900,000 | ||||||||||||||||||||||||
| Derivative Instruments, Gain (Loss) Recognized in Income, Net | $ 9,208,000 | $ (4,600,000) | $ (18,476,000) | $ 906,000 | $ 11,987,000 | $ 1,429,000 | $ (16,726,000) | $ 9,929,000 | $ 3,000,000 | $ 0 | $ 2,975,000 | ||||||||||||||