Derivatives (Outstanding Derivative Balances) (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Other Current Assets [Member]
Derivatives And Hedging Activities [Line Items]
Gross Derivative Balance	$ 51	$ 42
Cash Collateral	15	16
Total Derivative Balance	60	48
Netting	(6)	(10)
Other Noncurrent Assets [Member]
Derivatives And Hedging Activities [Line Items]
Gross Derivative Balance	81	99
Cash Collateral	0	0
Total Derivative Balance	77	95
Netting	(4)	(4)
Other Current Liabilities [Member]
Derivatives And Hedging Activities [Line Items]
Gross Derivative Balance	(57)	(122)
Cash Collateral	6	69
Total Derivative Balance	(45)	(43)
Netting	6	10
Other Noncurrent Liabilities [Member
Derivatives And Hedging Activities [Line Items]
Gross Derivative Balance	(87)	(110)
Cash Collateral	0	2
Total Derivative Balance	(83)	(104)
Netting	4	4
Gross Derivative Balance [Member]
Derivatives And Hedging Activities [Line Items]
Gross Derivative Balance	(12)	(91)
Netting [Member]
Derivatives And Hedging Activities [Line Items]
Netting	0	0
Cash Collateral [Member
Derivatives And Hedging Activities [Line Items]
Cash Collateral	21	87
Total Derivatve Balance [Member]
Derivatives And Hedging Activities [Line Items]
Total Derivative Balance	$ 9	$ (4)