Fair Value of Financial Instruments (Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation) (Details) (USD $) In Millions	3 Months Ended	6 Months Ended
Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Fair Value of Financial Instruments
Beginning balance - January 1	$ 68.1	$ 171.0	$ 45.6	$ 63.2
Total gains (losses)
Included in earnings	46.5	437.7	91.1	799.8
Included in other comprehensive income
Settlements	(30.6)	(369.8)	(52.7)	(624.1)
Transfers out of Level 3	(20.0)		(20.0)
Ending balance - March 31	64.0	238.9	64.0	238.9
Total gains (losses) for the period included in earnings attributable to the change in unrealized gains or losses on assets and liabilities still held at the reporting date	$ 46.5	$ 400.9	$ 91.1	$ 639.8

Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Abstract]

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- Definition

Fair Value Measurement with Unobservable Inputs Reconciliation Recurring Basis Asset and Liabilities, Change in Unrealized Gains Losses Included in Earnings on Instruments Still Held

+ Details

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- Definition

Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset and Liabilities, Included in Earnings

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- Definition

Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset and Liabilities, Included in Other Comprehensive Income

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- Definition

Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset and Liabilities, Settlements

+ Details

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- Definition

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Transfers Into Level Three

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- Definition

This element represents an asset measured at fair value using significant unobservable inputs (Level 3) which is required for reconciliation purposes of beginning and ending balances.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 157
-Paragraph 32
-Subparagraph c
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6925170&loc=d3e19207-110258

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