Employee Benefit Plans - Other Post Retirement Benefit Plans Components of Net Periodic Benefit Cost (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
U.S. Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost benefit earned	$ 4	$ 4	$ 14	$ 14
Interest cost on benefit obligation	7	6	19	18
Expected return on plan assets	(9)	(10)	(29)	(31)
Amortization of loss	1	2	5	7
Net periodic cost	3	2	9	8
Canadian Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost benefit earned	8	8	23	24
Interest cost on benefit obligation	10	11	32	33
Expected return on plan assets	(16)	(16)	(48)	(50)
Amortization of loss	5	6	14	19
Amortization of prior service cost	0	0	1	1
Net periodic cost	7	9	22	27
U.S. Other Post-Retirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost benefit earned	0	1	0	1
Interest cost on benefit obligation	2	1	6	5
Expected return on plan assets	(2)	(1)	(4)	(4)
Net periodic cost	0	1	2	2
Canadian Other Post-Retirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost benefit earned	1	1	2	3
Interest cost on benefit obligation	1	1	3	3
Net periodic cost	$ 2	$ 2	$ 5	$ 6