Financial Instruments: (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Fair value of financial instruments, details:
Carrying amount of long-term debt	$ 24,672		$ 24,088
Fair value of long-term debt	27,449		27,119
Debt and Marketable Equity Securities.
Debt securities - noncurrent, Adjusted Cost	7		8
Debt securities - noncurrent, gross unrealized gains	3		2
Available-for-sale equity investments, Adjusted Cost	10		31
Available-for-sale equity investments, gross unrealized gains	4		4
Available-for-sale equity investments, gross unrealized losses			(1)
Debt securities - noncurrent	10		10
Available-for-sale equity investments	14		34
Sales of debt and available-for-sale equity investments
Proceeds	18	45
Gross realized gains (before taxes)	3	14
Gross realized losses (before taxes)	(4)	0
Unrealized holding gains/(losses) on available-for-sale debt and equity securities
Net unrealized gains/(losses) arising during the period	(1)	15
Net unrealized (gains)/losses reclassified to net income	0	(8)
Writedowns included in net income for the period	$ 0	$ 0
Maximum contractual maturities of substantially all available-for-sale debt securities	1 year

This describes the maximum time frame of the contract terms of the entity's available-for-sale debt securities.

No definition available.

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This element represents the fair value of available-for-sale debt securities which mature after one year.

+ References

No definition available.

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This element represents the adjusted cost of investments accounted for other than equity method, that are considered available-for-sale and recorded at fair value.

+ References

No definition available.

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Represents the fair value of investments accounted for using other than equity method of accounting.

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No definition available.

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This item represents the gross unrealized gains for investments in alliances which are accounted for other than equity method investments. Such investments are intended to be held for more than one year.

+ References

No definition available.

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This item represents the gross unrealized losses for investments accounted using other than equity method.

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No definition available.

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This element represents the adjusted cost of debt securities intended to be held for more than one year, that are considered available-for-sale and recorded at fair value.

+ References

No definition available.

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This item represents the gross unrealized gains for debt securities which are intended to be held for more than one year.

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No definition available.

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Appreciation or loss in value (before reclassification adjustment) of the total of unsold securities during the period being reported on, net of tax and subsequent changes in previously impaired securities arising during the period. Reclassification adjustments include: (1) the unrealized holding gain (loss), net of tax, at the date of the transfer for a debt security from the held-to-maturity category transferred into the available-for-sale category. Also includes the unrealized gain (loss) at the date of transfer for a debt security from the available-for-sale category transferred into the held-to-maturity category; (2) the unrealized gains (losses) realized upon the sale of securities, after tax; and (3) the unrealized gains (losses) realized upon the write-down of securities, after tax.

+ References

No definition available.

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This item represents the gross profit realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

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The total amount of proceeds received for the sale of securities, categorized neither as held-to-maturity nor trading securities, during the reporting period.

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This item represents the gross loss realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

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The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

+ References

No definition available.

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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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Net of tax amount of the income statement impact of the reclassification adjustment for unrealized gain (loss) realized upon the sale of available-for-sale securities.

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Net of tax amount of the income statement impact of the reclassification adjustment for unrealized (losses) realized upon the write-down of available-for-sale securities.

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