Accumulated Other Comprehensive Loss - Reclassification (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other, net									$ (8)	$ (50)	$ (7)
Income before income taxes									2,191	1,822	1,060
Tax (expense) benefit									(242)	(642)	(308)
Consolidated net income	$ 903	$ 388	$ 361	$ 297	$ 334	$ 304	$ 286	$ 256	1,949	1,180	752
Derivative Instruments [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income before income taxes									(12)	(31)	35
Tax (expense) benefit									5	12	(14)
Consolidated net income									(7)	(19)	21
Derivative Instruments [Member] | Interest Rate Swaps [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest expense, net									(11)	(10)	(12)
Derivative Instruments [Member] | Treasury Lock [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest expense, net									$ (1)	(1)	(4)
Derivative Instruments [Member] | Foreign Currency Derivatives [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other, net										$ (20)	$ 51