Retirement and Benefit Plans (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, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule Of Pension And Other Postretirment Benefits Recgonized In Accumulated Other Comprehensive Income (Loss)
Interest cost	$ 8	$ 9	$ 9
Expected return on assets	(10)	(11)	(13)
Amortization of net actuarial loss	7	11	10
Settlement	4	7	7
Net periodic benefit cost	9	16	13
Net actuarial loss (gain)	(1)	2	9
Amortization of net actuarial loss	(7)	(11)	(10)
Settlement	(4)	(7)	(7)
Total recognized in other comprehensive income	(12)	(16)	(8)
Total recognized in net periodic benefit cost and other comprehensive income	$ (3)	$ 0	$ 5