Debt (Estimated Fair Value of Significant Financial Instruments) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term debt	$ 640	$ 334
Long-term debt	3,379	2,621
Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term debt	776	334
Long-term debt	$ 3,500	$ 2,819