Benefit Plans - Reconciliation of Benefit Obligations and Plan Assets (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pension Benefits [Member]
Change in benefit obligation:
Benefit obligation, beginning balance	$ 3,131	$ 3,227
Acquisitions	103
Service cost	8	8	$ 12
Interest cost	119	128	127
Amendments		1
Actuarial (gain) loss	100	72
Benefits paid from plan assets	(192)	(188)
Settlements	(37)	(101)
Foreign exchange	10	(16)
Benefit obligation, ending balance	3,242	3,131	3,227
Change in plan assets:
Fair value of plan assets, beginning balance	2,423	2,500
Acquisitions	75
Actual return on plan assets	247	211
Company contributions	51	19
Benefits paid from plan assets	(192)	(188)
Settlements	(37)	(103)
Foreign exchange	10	(16)
Fair value of plan assets, ending balance	2,577	2,423	2,500
Funded status	(665)	(708)
Amounts recognized in the Consolidated Balance Sheets consist of:
Other assets	4	4
Other liabilities	(669)	(712)
Net amount recognized	(665)	(708)
Other Postretirement Benefits [Member]
Change in benefit obligation:
Benefit obligation, beginning balance	66	82
Acquisitions	0
Service cost	1	1	1
Interest cost	2	3	3
Plan participants' contributions	5	5
Amendments	0
Actuarial (gain) loss	(1)	(13)
Benefits paid from plan assets	(11)	(12)
Settlements	0
Foreign exchange	0
Benefit obligation, ending balance	62	66	82
Change in plan assets:
Fair value of plan assets, beginning balance	86	86
Actual return on plan assets	5	3
Company contributions	3	4
Plan participants' contributions	5	5
Benefits paid from plan assets	(11)	(12)
Fair value of plan assets, ending balance	88	86	$ 86
Funded status	26	20
Amounts recognized in the Consolidated Balance Sheets consist of:
Other assets	47	44
Other liabilities	(21)	(24)
Net amount recognized	$ 26	$ 20