Financial Instruments (Estimated Fair Value of Debt, Financing and Capital Lease Obligations) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Dec. 17, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Exchangeable notes, related party	$ 80	$ 0	$ 800
Current and long-term debt, financing and capital lease obligations, Carrying amount	23,733	23,569
Exchangeable notes, fair value	80	0
Liabilities, Fair Value Disclosure, Nonrecurring	26,799	26,728
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Exchangeable notes, fair value	0	0
Liabilities, Fair Value Disclosure, Nonrecurring	17,399	17,506
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Exchangeable notes, fair value	0	0
Liabilities, Fair Value Disclosure, Nonrecurring	5,352	6,118
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Exchangeable notes, fair value	80	0
Liabilities, Fair Value Disclosure, Nonrecurring	$ 4,048	$ 3,104