Debt (details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014 item	Dec. 31, 2013
Debt disclosure
Commercial paper amount	$ 100us-gaap_CommercialPaper	$ 100us-gaap_CommercialPaper
5.50% Senior notes due December 1, 2015	400us-gaap_SeniorNotesCurrent
Total short-term debt	500us-gaap_DebtCurrent	100us-gaap_DebtCurrent
Total long-term debt	5,861us-gaap_LongTermDebtNoncurrent	6,261us-gaap_LongTermDebtNoncurrent
Total debt principal	6,361	6,361
Unamortized fair value adjustment, debt	50	51
Unamortized debt issuance costs	(62)us-gaap_UnamortizedDebtIssuanceExpense	(66)us-gaap_UnamortizedDebtIssuanceExpense
Total debt	6,349us-gaap_DebtAndCapitalLeaseObligations	6,346us-gaap_DebtAndCapitalLeaseObligations
Number of junior subordinated debentures that are not fixed-to-floating rate debentures	3
Number of separate trusts that issued preferred securities and used proceeds to purchase the Company's subordinated debentures that are not fixed-to-floating rate	3
Impact of amortization of the fair value adjustment on interest expense	1	1
Amount of debt obligations, other than commercial paper, due in 2015	400
Amount of debt obligations, other than commercial paper, due in 2016	400
Amount of debt obligations, other than commercial paper, due in 2017	450
Amount of debt obligations, other than commercial paper, due in 2018	500
Amount of debt obligations, other than commercial paper, due in 2019	$ 500

The reduction to interest expense as a result of amortization of the fair value adjustment.

No definition available.

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- Definition

The number of junior subordinated debentures that re not fixed-to-floating rate debentures.

+ References

No definition available.

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- Definition

The number of separate trusts that issued preferred securities and used proceeds to purchase the Company's subordinated debentures that are not fixed-to-floating rate.

+ References

No definition available.

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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.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 16

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-Topic 210

-SubTopic 10

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-Subparagraph (SX 210.5-02.19(a)(3))

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- Definition

Sum of the carrying values as of the balance sheet date of all debt, including all short-term borrowings, long-term debt, and capital lease obligations.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

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-Subparagraph (SX 210.7-03.16)

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-Subparagraph (SX 210.9-03.13,16)

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- Definition

Amount of short-term debt and current maturity of long-term debt and capital lease obligations due within one year or the normal operating cycle, if longer.

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- Definition

Represents the aggregate of total long-term debt, including current maturities and short-term debt.

+ References

No definition available.

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- Definition

Total fresh-start adjustment to long-term debt.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 852

-SubTopic 10

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-Subparagraph (a)

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- Definition

Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

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-Topic 235

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-Subparagraph (SX 210.12-04.(a))

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- Definition

Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

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Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the fourth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

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Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the third fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the second fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Carrying amount of long-term debt, net of unamortized discount or premium, excluding amounts to be repaid within one year or the normal operating cycle, if longer (current maturities). Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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- Definition

Carrying value as of the balance sheet date of the portion of long-term notes having the highest claim on the assets of the issuer in case of bankruptcy or liquidation, due within one year or the normal operating cycle, if longer. Senior note holders are paid off in full before any payments are made to debt holders having a lesser priority of repayment.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

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-Subparagraph (SX 210.5-02.20)

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- Definition

The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.

+ References

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