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Segments (Narrative) (Details) (USD $)
In Millions, unless otherwise specified
 3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Segment Reporting Information [Line Items]    
Operating revenue $ 9,388us-gaap_Revenues $ 8,916us-gaap_Revenues
Exchanged products | Intersegment Sales/Other    
Segment Reporting Information [Line Items]    
Operating revenue $ (782)us-gaap_Revenues
/ us-gaap_ProductOrServiceAxis
= us-gaap_ExchangeOfProductiveAssetsMember
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_IntersegmentEliminationMember		 [1] $ (1,003)us-gaap_Revenues
/ us-gaap_ProductOrServiceAxis
= us-gaap_ExchangeOfProductiveAssetsMember
/ us-gaap_StatementBusinessSegmentsAxis
= us-gaap_IntersegmentEliminationMember		 [1]
[1] Represents value of products delivered under exchange agreements with third parties, as discussed above, determined on a market price basis.