Debt, Accounts Receivable Sales Facility and Capitalized Interest (Details) - USD ($)	1 Months Ended	3 Months Ended		6 Months Ended
	Jul. 31, 2015	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Capitalized Interest (Textual)
Interest costs incurred, capitalized		$ 16,000,000	$ 18,000,000	$ 32,000,000	$ 35,000,000
Credit Facilities [Member] | A/R Sales Facility [Member]
Accounts Receivable Sales Facility (Textual)
Line of credit facility, maximum borrowing capacity		1,500,000,000		1,500,000,000
Amount outstanding		$ 100,000,000		$ 100,000,000		$ 100,000,000
Credit Facilities [Member] | A/R Sales Facility [Member] | Subsequent Event [Member]
Accounts Receivable Sales Facility (Textual)
Line of credit facility, maximum borrowing capacity	$ 1,400,000,000
Maturity date of accounts receivable sales facility	Jul. 31, 2016