Fair Value Disclosure (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2012 Minimum	Dec. 31, 2012 Maximum	Dec. 31, 2012 Input Level 2, Fair Value	Dec. 31, 2011 Input Level 2, Fair Value	Dec. 31, 2012 Carrying Amount Input Level 2, Fair Value	Dec. 31, 2011 Carrying Amount Input Level 2, Fair Value
Liabilities
Long-term debt excluding capital lease obligations				$ 8,019	$ 8,352	$ 7,513	$ 8,149
Fair value related additional information
Discount rates used in valuations (as a percent)	6.00%	7.50%	9.50%