Pension and Postretirement Benefits - Fair Value of Plan Assets by Investment Category (Detail) - USD ($) $ in Millions	Dec. 31, 2019		Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Total Investments	$ 1,267		$ 1,153
U.S. Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Investments	400		377
International Government Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Investments	254	[1]	245
International Corporate Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Investments	99	[2]	94
International Mortgage Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Investments	66	[3]	69
All Other Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Investments	46	[4]	41
U.S. Equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Investments	73		57
International Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Investments	197	[5]	157
Emerging Markets Growth Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Investments	16		13
U.S. Equity Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Investments	15		12
Asset Allocation Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Investments	86	[6]	74
Cash and Accrued Items [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Investments	15		14
Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Investments	256		219
Level 1 [Member] | U.S. Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Investments	168		148
Level 1 [Member] | U.S. Equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Investments	73		57
Level 1 [Member] | Cash and Accrued Items [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Investments	15		14
Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Investments	1,007		928
Level 2 [Member] | U.S. Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Investments	228		223
Level 2 [Member] | International Government Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Investments	254	[1]	245
Level 2 [Member] | International Corporate Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Investments	99	[2]	94
Level 2 [Member] | International Mortgage Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Investments	66	[3]	69
Level 2 [Member] | All Other Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Investments	46	[4]	41
Level 2 [Member] | International Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Investments	197	[5]	157
Level 2 [Member] | Emerging Markets Growth Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Investments	16		13
Level 2 [Member] | U.S. Equity Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Investments	15		12
Level 2 [Member] | Asset Allocation Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Investments	86	[6]	74
Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Investments	4		6
Level 3 [Member] | U.S. Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total Investments	$ 4		$ 6

[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.