Fair Value (Recurring Measurements) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Fair Value Assets And Liabilities Measured On Recurring Basis Abstract
Available-for-sale securities	$ 681	$ 1,340
Trading securities	12	12
Derivatives	100	120
Total assets	793	1,472
Derivatives	657	690
Total liabilities	657	690
Level 1
Fair Value Assets And Liabilities Measured On Recurring Basis Abstract
Available-for-sale securities	0	1
Trading securities	12	12
Derivatives	0	2
Total assets	12	15
Derivatives	0	0
Total liabilities	0	0
Level 2
Fair Value Assets And Liabilities Measured On Recurring Basis Abstract
Available-for-sale securities	681	1,339
Trading securities	0	0
Derivatives	18	52
Total assets	699	1,391
Derivatives	179	476
Total liabilities	179	476
Level 3
Fair Value Assets And Liabilities Measured On Recurring Basis Abstract
Available-for-sale securities	0	0
Trading securities	0	0
Derivatives	82	66
Total assets	82	66
Derivatives	478	214
Total liabilities	$ 478	$ 214

This element represents the portion of the balance sheet assertion valued at fair value by the entity 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. This item represents Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

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Derivative instrument obligations meeting the definition of a liability which the Company is a party to as of the balance sheet date.

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- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity 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. This item represents Trading Securities which consist of all investments in certain debt and equity securities that are bought and held principally for the purpose of selling them in the near term (thus held for only a short period of time) or for which an entity has elected the fair value option. Trading generally reflects active and frequent buying and selling, and trading securities are generally used with the objective of generating profits on short-term differences in price, but this category of investments may also include items which are not intended to be sold in the near term or for which the fair value option has been elected.

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