Fair Value Measurements and Derivatives - Fair Value of Financial Instrument (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Carrying Value	$ 1,606	$ 1,659
Fair Value	1,676	1,720
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Market Approach Valuation Technique [Member] | Senior Notes Total [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Carrying Value	1,525	1,580
Fair Value	1,600	1,643
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Income Approach Valuation Technique [Member] | Other indebtedness [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Carrying Value	81	79
Fair Value	$ 76	$ 77