Expected Cash Flows for the Pension Benefit and Other Postretirement Benefit Plans (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($)
Pension Plan [Member]
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months	$ 183	[1]
Defined Benefit Plan, Expected Future Benefit Payments, Year Two	168	[1]
Defined Benefit Plan, Expected Future Benefit Payments, Year Three	166	[1]
Defined Benefit Plan, Expected Future Benefit Payments, Year Four	165	[1]
Defined Benefit Plan, Expected Future Benefit Payments, Year Five	165	[1]
Defined Benefit Plan, Expected Future Benefit Payments, Five Fiscal Years Thereafter	812	[1]
Pension Plan [Member] | Plan Trusts [Member]
Defined Benefit Plans, Estimated Future Employer Contributions in Next Fiscal Year	0	[1]
Pension Plan [Member] | Plan Participants
Defined Benefit Plans, Estimated Future Employer Contributions in Next Fiscal Year	11	[1],[2]
Other Postretirement Benefit Plan [Member]
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months	6	[3]
Defined Benefit Plan, Expected Future Benefit Payments, Year Two	6	[3]
Defined Benefit Plan, Expected Future Benefit Payments, Year Three	5	[3]
Defined Benefit Plan, Expected Future Benefit Payments, Year Four	5	[3]
Defined Benefit Plan, Expected Future Benefit Payments, Year Five	4	[3]
Defined Benefit Plan, Expected Future Benefit Payments, Five Fiscal Years Thereafter	19	[3]
Other Postretirement Benefit Plan [Member] | Plan Trusts [Member]
Defined Benefit Plans, Estimated Future Employer Contributions in Next Fiscal Year	0	[3]
Other Postretirement Benefit Plan [Member] | Plan Participants
Defined Benefit Plans, Estimated Future Employer Contributions in Next Fiscal Year	$ 0	[2],[3]

[1] Based on the funding status and ERISA limitations, the Company anticipates contributions to the Retirement Plan will not be required during 2017.

[2] The expected benefit payments for the SERP will be paid directly from the Company's corporate assets.

[3] Expected payments under other postretirement benefit plans are shown net of participant contributions.