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Debt (Fair Value of Debt) (Details) (USD $)
In Millions, unless otherwise specified |
Dec. 31, 2012
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Dec. 31, 2011
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Portion at Fair Value, Fair Value Disclosure [Member]
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| Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | ||||||
| Notes Payable, Fair Value Disclosure | $ 5,863 | $ 6,219 | ||||
| Notes Payable, Other Payables, Disclosure | 1,599 | [1] | 1,467 | [1] | ||
| Loans Payable, Fair Value Disclosure | 2,489 | 1,615 | ||||
| Subsidiaries Notes Disclosure | 1,075 | 1,070 | ||||
| Debt Excluding Capital Leases | 11,026 | 10,371 | ||||
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Carrying (Reported) Amount, Fair Value Disclosure [Member]
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| Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | ||||||
| Notes Payable, Fair Value Disclosure | 5,303 | 5,892 | ||||
| Notes Payable, Other Payables, Disclosure | 1,629 | [1] | 1,504 | [1] | ||
| Loans Payable, Fair Value Disclosure | 2,463 | 1,646 | ||||
| Subsidiaries Notes Disclosure | 978 | 972 | ||||
| Debt Excluding Capital Leases | $ 10,373 | $ 10,014 | ||||
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