Retirement and Benefit Plans (Defined Benefit Retirement Plans with Overfunded and Underfunded Status) (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Change In Fair Value Roll Forward
Fair value of plan assets at January 1	[1]	$ 172
Fair value of plan assets at December 31	[1]	185	$ 172
Defined Benefit Plan, Change in Benefit Obligation
Interest cost		8	9	$ 9
Underfunded defined benefit pension plans
Defined Benefit Plan Change In Fair Value Roll Forward
Fair value of plan assets at January 1		172	166
Actual return on assets		28	11
Contributions		6	20
Settlement		(11)	(15)
Benefits paid		(10)	(10)
Fair value of plan assets at December 31		185	172	166
Defined Benefit Plan, Change in Benefit Obligation
Projected benefit obligation at January 1		206	220
Interest cost		8	9
Settlement		(11)	(15)
Actuarial (gain) loss		16	2
Benefits paid		(10)	(10)
Projected benefit obligation at December 31		209	206	$ 220
Underfunded projected benefit obligation at December 31		(24)	(34)
Accumulated benefit obligation at December 31	[2]	$ 209	$ 206

[1] For further information on fair value hierarchy levels, refer to Note 1 .

[2] (a) Since the Plan’s benefits are frozen , the rate of compensation increase is no longer an assumption used to calculate the accumulated benefit obligation. Therefore, the accumulated benefit obligation was the same as the projected benefit obligation at both December 31, 2017 and 2016 .