Defined Benefit Plan, Change in Obligations and Fair Value (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
Defined Benefit Plan, Plan Assets, Amount		$ 3,017		$ 3,432
Defined Benefit Plan, Funded (Unfunded) Status of Plan		484		464
Pension Plan [Member]
Defined Benefit Plan, Benefit Obligation	[2]	2,468	[1]	2,910	[1]	$ 2,747
Defined Benefit Plan, Service Cost	[3]	6	[2]	5	[2]	5
Defined Benefit Plan, Interest Cost		91	[2]	95	[2]	97
Defined Benefit Plan, Benefit Obligation, Contributions by Plan Participant	[2]	0		0
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)	[2]	(228)		225
Defined Benefit Plan, Benefit Obligation, Benefits Paid	[2]	(178)		(156)
Defined Benefit Plan, Benefit Obligation, Administrative Expenses	[2]	(6)		(6)
Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment	[2]	0		0
Defined Benefit Plan, Benefit Obligation, Special and Contractual Termination Benefits	[2]	0		0
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Settlement	[2]	(127)		0
Defined Benefit Plan, Plan Assets, Amount	[2]	2,885		3,288		3,016
Defined Benefit Plan, Plan Assets, Increase (Decrease) for Actual Return (Loss)	[2]	(100)		425
Defined Benefit Plan, Plan Assets, Contributions by Employer	[2]	8		9
Defined Benefit Plan, Plan Assets, Contributions by Plan Participant	[2]	0		0
Defined Benefit Plan, Plan Assets, Benefits Paid	[2]	(178)		(156)
Defined Benefit Plan, Plan Assets, Administration Expense	[2]	(6)		(6)
Defined Benefit Plan, Plan Assets, Payment for Settlement	[2]	(127)		0
Defined Benefit Plan, Funded (Unfunded) Status of Plan	[2],[4]	$ 417		$ 378
Defined Benefit Plan, Funded Percentage	[2]	117.00%		113.00%
Defined Benefit Plan, Accumulated Benefit Obligation	[2]	$ 2,468		$ 2,910
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	[2]	4.27%		3.62%
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan, Benefit Obligation		$ 51		$ 58		58
Defined Benefit Plan, Service Cost		0		0		0
Defined Benefit Plan, Interest Cost		1		1		2
Defined Benefit Plan, Benefit Obligation, Contributions by Plan Participant		5		4
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)		(2)		(1)
Defined Benefit Plan, Benefit Obligation, Benefits Paid		(11)		(8)
Defined Benefit Plan, Benefit Obligation, Administrative Expenses		0		0
Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment		0		(5)
Defined Benefit Plan, Benefit Obligation, Special and Contractual Termination Benefits		0		9
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Settlement		0		0
Defined Benefit Plan, Plan Assets, Amount		155		164		$ 157
Defined Benefit Plan, Plan Assets, Increase (Decrease) for Actual Return (Loss)		(3)		11
Defined Benefit Plan, Plan Assets, Contributions by Employer	[5]	0		0
Defined Benefit Plan, Plan Assets, Benefits Paid		(11)		(8)
Defined Benefit Plan, Plan Assets, Administration Expense		0		0
Defined Benefit Plan, Plan Assets, Payment for Settlement		0		0
Defined Benefit Plan, Funded (Unfunded) Status of Plan	[6]	$ 104		$ 106
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate		3.96%		3.29%
Valuation, Market Approach [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan, Plan Assets, Contributions by Plan Participant		$ 5		$ 4

[1] Includes $68 million and $78 million of benefit obligations for the unfunded nonqualified supplemental pension plans at December 31, 2018 and 2017, respectively.

[2] Employer contributions represent the benefits that were paid to nonqualified plan participants. Unfunded nonqualified supplemental pension plans are not funded through plan assets.

[3] Administrative fees are recognized in service cost for each of the periods presented.

[4] Pension benefits included assets of $485 million and $456 million, and liabilities of $68 million and $78 million, at December 31, 2018 and 2017, respectively, recorded in Other assets in the Consolidated Balance Sheets.

[5] The Company contributed less than $1 million to the other postretirement benefits plans during both 2018 and 2017.

[6] Other postretirement benefits included assets of $104 million and $106 million at December 31, 2018 and 2017, respectively, recorded in Other assets in the Consolidated Balance Sheets.