Fair Value Fair Value (Details 4) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Fair Value of Financial Instruments [Line Items]
Notes Receivable Excudling Capital Leases	$ 37	$ 39
Dividends Payable, Current	108	107
Short-term Debt	0	240
Long-term Debt	8,046	7,813
Fair Value, Inputs, Level 1 [Member]
Fair Value of Financial Instruments [Line Items]
Notes Receivable, Fair Value Disclosure	0	0
Dividends Payable Fair Value Disclosure	108	107
Notes Payable, Fair Value Disclosure	0	0
Long-term Debt, Fair Value	513	507
Fair Value, Inputs, Level 2 [Member]
Fair Value of Financial Instruments [Line Items]
Notes Receivable, Fair Value Disclosure	0	0
Dividends Payable Fair Value Disclosure	0	0
Notes Payable, Fair Value Disclosure	0	240
Long-term Debt, Fair Value	7,441	7,453
Fair Value, Inputs, Level 3 [Member]
Fair Value of Financial Instruments [Line Items]
Notes Receivable, Fair Value Disclosure	37	39
Dividends Payable Fair Value Disclosure	0	0
Notes Payable, Fair Value Disclosure	0	0
Long-term Debt, Fair Value	$ 1,089	$ 933