Accumulated Other Comprehensive Income - Reclassification of Component of Accumulated Other Comprehensive Income (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Derivative Instruments, Gain (Loss) [Line Items]
Interest expense	$ (121)	$ (121)
Other, net	(3)	(11)
Operating revenues	3,396	3,336
Gains and losses on cash flow hedges, Total before tax	336	262
Gains and losses on cash flow hedges, Tax (expense) benefit	(99)	(86)
Total reclassifications for the period, Net of tax	237	176
Amount Reclassified from Accumulated Other Comprehensive Income [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains and losses on cash flow hedges, Total before tax	2	1
Gains and losses on cash flow hedges, Tax (expense) benefit	(1)
Total reclassifications for the period, Net of tax	1	1
Interest Rate Swaps [Member] | Amount Reclassified from Accumulated Other Comprehensive Income [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Interest expense	(1)	(2)
Treasury rate locks [Member] | Amount Reclassified from Accumulated Other Comprehensive Income [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Interest expense	(1)
Foreign currency derivatives[Member] | Amount Reclassified from Accumulated Other Comprehensive Income [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Other, net	13	8
Electricity commodity derivatives [Member] | Amount Reclassified from Accumulated Other Comprehensive Income [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Operating revenues	$ (9)	$ (5)