Financial Instruments (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Carrying Amount
Carrying amounts and estimated fair values of financial instruments
Long-term debt	$ 4,039	$ 4,346
Derivative instruments	109	165
Fair Value
Carrying amounts and estimated fair values of financial instruments
Long-term debt	4,451	4,690
Derivative instruments	$ 109	$ 165