Net Periodic Benefit Cost and Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Schedule Of Pension And Other Postretirment Benefits Recgonized In Accumulated Other Comprehensive Income (Loss) [Abstract]
Interest cost	$ 9	$ 10	$ 10
Expected return on assets	(13)	(14)	(13)
Amortization of net actuarial loss	10	7	11
Settlement	7	5	5
Net periodic benefit cost	13	8	13
Net actuarial gain (loss) arising during the period	9	37	(38)
Amortization of net actuarial loss	(10)	(7)	(11)
Settlement	(7)	(5)	(5)
Total recognized in other comprehensive income	(8)	25	(54)
Total recognized in net periodic benefit cost and other comprehensive income	$ 5	$ 33	$ (41)