Derivatives (Outstanding Derivative Balances) (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Derivatives And Hedging Activities [Line Items]
Gross Derivative Balance	$ (555)	$ (720)
Cash Collateral	345	478
Total Derivative Balance	(210)	(242)
Other Current Assets [Member]
Derivatives And Hedging Activities [Line Items]
Gross Derivative Balance	52	54
Netting	(32)	(39)
Cash Collateral	96	103
Total Derivative Balance	116	118
Other Noncurrent Assets [Member]
Derivatives And Hedging Activities [Line Items]
Gross Derivative Balance	101	113
Netting	(50)	(59)
Total Derivative Balance	51	54
Other Current Liabilities [Member]
Derivatives And Hedging Activities [Line Items]
Gross Derivative Balance	(399)	(489)
Netting	32	39
Cash Collateral	212	274
Total Derivative Balance	(155)	(176)
Other Noncurrent Liabilities [Member]
Derivatives And Hedging Activities [Line Items]
Gross Derivative Balance	(309)	(398)
Netting	50	59
Cash Collateral	37	101
Total Derivative Balance	$ (222)	$ (238)