Debt (Details) (USD $)	9 Months Ended
Sep. 30, 2011	Dec. 31, 2010
Debt Type Details [Abstract]
Commercial Paper	$ 100,000,000	$ 100,000,000
Long Term Debt Current	230,000,000	452,000,000
Total short-term debt	330,000,000	552,000,000
Long-term debt	2,883,000,000	2,288,000,000
Percentage of principal amount to be redeemed	100.00%
Debt Text Details [Abstract]
Revolving Credit and Letter of Credit Agreement	1,500,000,000
Revolving Credit and Letter of Credit Agreement Term	5
Revolving Credit and Letter of Credit Agreement - Available for Letters of Credit	500,000,000
Revolving Credit and Letter of Credit Agreement - Number of Banks Diversified Among	16
Revolving Credit and Letter of Credit Agreement - Three Banks Percentage Commitment	12.00%
Revolving Credit and Letter of Credit Agreement - 13 Banks Remaining Percentage Commitment	64.00%
Revolving Credit and Letter of Credit Agreement - Option to Increase Commitment Amount	2,000,000,000
Revolving Credit and Letter of Credit Agreement - Covenants	maintain a total debt to adjusted capital ratio at or below 0.50 to 1.00
Revolving Credit and Letter of Credit Agreement - Borrowing Capacity	1,400,000,000
Revolving Credit and Letter of Credit Agreement - Additional Borrowing Capacity	4,800,000,000
Total Debt Outstanding	3,200,000,000
Letters of Credit Issued	118,000,000
Other Long Term Debt [Member]
Debt Type Details [Abstract]
Long-term debt	29,000,000	30,000,000
Notes Due 20175375 Interest [Member]
Debt Type Details [Abstract]
Long-term debt	250,000,000	250,000,000
Notes Due 2018635 Interest [Member]
Debt Type Details [Abstract]
Long-term debt	131,000,000	131,000,000
Notes Due 201985 Interest [Member]
Debt Type Details [Abstract]
Long-term debt	251,000,000	251,000,000
Notes Due 20204375 Interest [Member]
Debt Type Details [Abstract]
Long-term debt	249,000,000	249,000,000
Notes Due 20205125 Interest [Member]
Debt Type Details [Abstract]
Long-term debt	299,000,000	299,000,000
Notes Due 202145 Interest [Member]
Debt Type Details [Abstract]
Long-term debt	298,000,000	0
Effective interest rate	4.683%
Basis Points Added To Treasury Rate	20
Long Term Debt Face Value	300,000,000
Interest rate of long term debt issued	4.50%
Notes Due 2021637 Interest [Member]
Debt Type Details [Abstract]
Long-term debt	78,000,000	78,000,000
Notes Due 2023765 Interest [Member]
Debt Type Details [Abstract]
Long-term debt	100,000,000	100,000,000
Notes Due 202383 Interest [Member]
Debt Type Details [Abstract]
Long-term debt	17,000,000	17,000,000
Debentures Due 20277875 Interest [Member]
Debt Type Details [Abstract]
Long-term debt	300,000,000	300,000,000
Step Down Notes Due 203383 Interest [Member]
Debt Type Details [Abstract]
Long-term debt	83,000,000	83,000,000
Notes Due 2036615 Interest [Member]
Debt Type Details [Abstract]
Long-term debt	500,000,000	500,000,000
Notes Due 20415875 Interest [Member]
Debt Type Details [Abstract]
Long-term debt	298,000,000	0
Effective interest rate	6.008%
Basis Points Added To Treasury Rate	25
Long Term Debt Face Value	$ 300,000,000
Interest rate of long term debt issued	5.875%

The Company may redeem Notes at any time, in whole or in part, at a redemption price equal to the greater of 100% of the principal amount of the Notes to be redeemed or the present value of the remaining principal and interest payments on the Notes being redeemed discounted at the applicable treasury rate plus this amount of basis points.

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- Definition

Letters of credit issued

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Additional borrowing capacity under maximum debt coverage covenant under bank line facility.

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Face value of long term Notes payable

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The percentage of principal amount of a Note that the Company can redeem at any time, in whole or in part

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- Definition

Carrying value as of the balance sheet date of short-term borrowings using unsecured obligations issued by banks, corporations and other borrowers to investors. The maturities of these money market securities generally do not exceed 270 days.

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Interest rate stated in the contractual debt agreement.

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Description of the conditions for borrowing under the credit facility including the nature of any restrictions.

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Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

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Including current and noncurrent portions, aggregate carrying amount of long-term borrowings as of the balance sheet date. May include notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt, which had initial maturities beyond one year or beyond the normal operating cycle, if longer, and after deducting unamortized discount or premiums, if any.

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Total of the portions of the carrying amounts as of the balance sheet date of long-term debt, which may include notes payable, bonds payable, debentures, mortgage loans, and commercial paper, which are scheduled to be repaid within one year or the normal operating cycle, if longer, and after deducting unamortized discount or premiums, if any.

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Sum of the carrying amounts at the balance sheet date of short-term borrowings not otherwise specified in the taxonomy having initial terms less than one year or the normal operating cycle, if longer.

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