Pension and Postretirement Benefits - Fair Value of Plan Assets by Investment Category (Detail) - USD ($) $ in Millions		Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Total Investments		$ 1,153	$ 498
U.S. Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Investments		377	411
International Government Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Investments	[1]	245
International Corporate Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Investments	[2]	94
International Mortgage Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Investments	[3]	69
All Other Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Investments	[4]	41
U.S. Equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Investments		57	73
International Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Investments	[5]	157
Emerging Markets Growth Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Investments		13
U.S. Equity Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Investments		12
Asset Allocation Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Investments	[6]	74
Cash and Accrued Items [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Investments		14	14
Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Investments		219	247
Level 1 [Member] | U.S. Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Investments		148	160
Level 1 [Member] | U.S. Equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Investments		57	73
Level 1 [Member] | Cash and Accrued Items [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Investments		14	14
Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Investments		928	246
Level 2 [Member] | U.S. Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Investments		223	246
Level 2 [Member] | International Government Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Investments	[1]	245
Level 2 [Member] | International Corporate Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Investments	[2]	94
Level 2 [Member] | International Mortgage Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Investments	[3]	69
Level 2 [Member] | All Other Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Investments	[4]	41
Level 2 [Member] | International Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Investments	[5]	157
Level 2 [Member] | Emerging Markets Growth Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Investments		13
Level 2 [Member] | U.S. Equity Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Investments		12
Level 2 [Member] | Asset Allocation Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Investments	[6]	74
Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Investments		6	5
Level 3 [Member] | U.S. Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Investments		$ 6	$ 5

[1] Investments in predominately E.U. government securities and U.K. Treasury securities, with credit ratings primarily AAA.

[2] Investments in European and U.K. fixed interest securities, with credit ratings of primarily BBB and above.

[3] Investments in international mortgage funds.

[4] Investments predominantly in various international fixed income obligations that are individually insignificant.

[5] Investments in various funds that track international indices.

[6] Investments in fixed income securities, equities and alternative asset classes, including commodities and property assets.