Net Periodic Benefit Cost and Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Schedule Of Pension And Other Postretirment Benefits Recgonized In Accumulated Other Comprehensive Income (Loss) [Abstract]
Interest cost	$ 10	$ 10	$ 10
Expected return on assets	(14)	(13)	(13)
Amortization of net actuarial loss	7	11	14
Settlement	5	5	6
Net periodic pension cost	8	13	17
Net actuarial gain (loss) arising during the period	37	(38)	7
Amortization of net actuarial loss	(7)	(11)	(14)
Settlement	(5)	(5)	(6)
Total recognized in other comprehensive income	25	(54)	(13)
Total recognized in net periodic benefit cost and other comprehensive income	$ 33	$ (41)	$ 4