Segments - Narrative (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012		Jun. 30, 2012
Business Acquisition [Line Items]
Date of refinery purchase									Jun. 22, 2012
Refinery, purchase price															$ 180
Grants receivable															30
Total operating revenue	9,647	11,178	10,621	8,916	9,076	10,490	9,707	8,500	40,362		37,773		36,670
Exchanged products | Intersegment Eliminations
Business Acquisition [Line Items]
Total operating revenue									$ (5,104)	[1]	$ (5,352)	[1]	$ (1,121)	[1]

[1] Represents value of products delivered under our strategic agreements, as discussed above, determined on a market price basis.