Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
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Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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.

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The cash inflow from a borrowing with the highest claim on the assets of the entity in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle, if longer).

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Including the current and noncurrent portions, carrying value as of the balance sheet date of Notes with the highest claim on the assets of the issuer in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle if longer). Senior note holders are paid off in full before any payments are made to junior note holders.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 16
-Article 9

Reference 2: http://www.xbrl.org/2003/role/presentationRef
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Annual rate of quarterly payments under senior notes.

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Letter of credit facility existing limit.

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Letter of credit facility revised limit.

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Rate of Interest of Equity security units in public offering in order to fund payments relating to master agreement.

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Required Statutory Capital and Surplus for Principal Operating Subsidiares.

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Notes Payable and Debt and Financing Arrangements (Detail) (USD $)	6 Months Ended		12 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Dec. 31, 2010	Jun. 21, 2007
Proceeds from Issuance of Senior Long-term Debt	$ 600,000,000
Debt Instrument, Interest Rate, Effective Percentage	6.50%
Required Statutory Capital And Surplus For Principal Operating Subsidiares			6,200,000,000
Senior Notes	575,000,000
Equity Unit Note Coupon Rate	8.25%
Rate of interest of Equity security Units	10.75%	10.75%
Line of Credit Facility, Maximum Borrowing Capacity	1,000,000,000
Letter of credit facility existing limit				4,000,000,000
Letter of credit facility revised limit	$ 3,000,000,000