Debt, Long-term debt (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
Sep. 30, 2015	Dec. 31, 2014
Long-term debt [Line Items]
Long-term debt	$ 7,745	$ 6,761
Long-term debt, current portion	(3)	(4)
Long-term debt, noncurrent portion	$ 7,742	$ 6,757
Senior Notes due 2019, $2,000 million, 5.0% [Member]
Long-term debt [Line Items]
Maturity year	2019	2019
Face amount	$ 2,000	$ 2,000
Stated interest rate (in hundredths)	5.00%	5.00%
Long-term debt	$ 1,994	$ 1,993
Senior Notes due 2021, $1,000 million, 6.0% [Member]
Long-term debt [Line Items]
Maturity year	2021	2021
Face amount	$ 1,000	$ 1,000
Stated interest rate (in hundredths)	6.00%	6.00%
Long-term debt	$ 1,000	$ 1,000
Senior Notes due 2024, $1,000 million, 5.75% [Member]
Long-term debt [Line Items]
Maturity year	2024	2024
Face amount	$ 1,000	$ 1,000
Stated interest rate (in hundredths)	5.75%	5.75%
Long-term debt	$ 1,000	$ 1,000
Senior Notes due 2055, $1,000 million, 4.625% ($16 million of discount) [Member]
Long-term debt [Line Items]
Maturity year	2055
Face amount	$ 1,000
Stated interest rate (in hundredths)	4.625%
Unamortized discount	$ 16
Long-term debt	$ 984
Guaranteed Notes due 2044, $1,000 million, 4.875% ($11 million of discount) [Member]
Long-term debt [Line Items]
Maturity year	2044	2044
Face amount	$ 1,000	$ 1,000
Stated interest rate (in hundredths)	4.875%	4.875%
Unamortized discount	$ 11
Long-term debt	$ 989	$ 988
Guaranteed Notes due 2023, $750 million, 4.0% ($8 million of discount) [Member]
Long-term debt [Line Items]
Maturity year	2023	2023
Face amount	$ 750	$ 750
Stated interest rate (in hundredths)	4.00%	4.00%
Unamortized discount	$ 8
Long-term debt	$ 742	$ 741
Guaranteed Notes due 2043, $750 million, 5.25% ($22 million of discount) [Member]
Long-term debt [Line Items]
Maturity year	2043	2043
Face amount	$ 750	$ 750
Stated interest rate (in hundredths)	5.25%	5.25%
Unamortized discount	$ 22
Long-term debt	$ 728	$ 728
Guaranteed Notes due 2027, $300 million, 8.1% [Member]
Long-term debt [Line Items]
Maturity year	2027	2027
Face amount	$ 300	$ 300
Stated interest rate (in hundredths)	8.10%	8.10%
Long-term debt	$ 300	$ 300
Other long-term debt [Member]
Long-term debt [Line Items]
Long-term debt	$ 8	$ 11

Year when the debt instrument is scheduled to be fully repaid.

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- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 55

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Contractual interest rate for funds borrowed, under the debt agreement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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The amount of debt discount that was originally recognized at the issuance of the instrument that has yet to be amortized.

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- Definition

Amount of long-term debt and capital lease obligation due after one year or beyond the normal operating cycle, if longer.

+ References

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

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-Subparagraph (SX 210.5-02.22)

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-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 6

-Section H

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Amount of long-term debt and capital leases due within one year or the normal operating cycle, if longer.

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Amount of long-term debt and capital lease obligations including current maturities.

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