Pension And Other Retirement Benefits - Summary of Pension Plan Assets by Category Based on Hierarchy of Fair Value Measurements (Detail) - Pension Plans - U.S. Plans - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Total assets	$ 395	$ 348	$ 357
Percent of total assets	100.00%	100.00%
Level 1
Defined Benefit Plan Disclosure [Line Items]
Total assets	$ 34	$ 21
Level 2
Defined Benefit Plan Disclosure [Line Items]
Total assets	311	271
Measured using NAV practical expedient
Defined Benefit Plan Disclosure [Line Items]
Total assets	50	56
Cash and cash equivalent
Defined Benefit Plan Disclosure [Line Items]
Total assets	$ 2	$ 1
Percent of total assets	1.00%	0.00%
Cash and cash equivalent | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total assets	$ 0	$ 0
Cash and cash equivalent | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total assets	2	1
Total equity investments
Defined Benefit Plan Disclosure [Line Items]
Total assets	$ 190	$ 161
Percent of total assets	48.00%	47.00%
Total equity investments | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total assets	$ 0	$ 0
Total equity investments | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total assets	190	161
U.S. large-cap
Defined Benefit Plan Disclosure [Line Items]
Total assets	$ 140	$ 122
Percent of total assets	35.00%	35.00%
U.S. large-cap | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total assets	$ 0	$ 0
U.S. large-cap | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total assets	140	122
U.S. small and mid-cap
Defined Benefit Plan Disclosure [Line Items]
Total assets	$ 21	$ 16
Percent of total assets	5.00%	5.00%
U.S. small and mid-cap | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total assets	$ 0	$ 0
U.S. small and mid-cap | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total assets	21	16
Emerging markets
Defined Benefit Plan Disclosure [Line Items]
Total assets	$ 29	$ 23
Percent of total assets	7.00%	7.00%
Emerging markets | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total assets	$ 0	$ 0
Emerging markets | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total assets	29	23
Total fixed-income investments
Defined Benefit Plan Disclosure [Line Items]
Total assets	$ 180	$ 165
Percent of total assets	46.00%	47.00%
Total fixed-income investments | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total assets	$ 34	$ 21
Total fixed-income investments | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total assets	119	109
Total fixed-income investments | Measured using NAV practical expedient
Defined Benefit Plan Disclosure [Line Items]
Total assets	27	35
Emerging markets bond fund
Defined Benefit Plan Disclosure [Line Items]
Total assets	$ 15	$ 13
Percent of total assets	4.00%	4.00%
Emerging markets bond fund | Measured using NAV practical expedient
Defined Benefit Plan Disclosure [Line Items]
Total assets	$ 15	$ 13
Intermediate-term investment grade U.S. government/ corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Total assets	$ 119	$ 109
Percent of total assets	30.00%	31.00%
Intermediate-term investment grade U.S. government/ corporate bonds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total assets	$ 0	$ 0
Intermediate-term investment grade U.S. government/ corporate bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total assets	119	109
U.S. Treasury Inflation-Protected Securities (TIPs)
Defined Benefit Plan Disclosure [Line Items]
Total assets	$ 22	$ 21
Percent of total assets	6.00%	6.00%
U.S. Treasury Inflation-Protected Securities (TIPs) | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total assets	$ 22	$ 21
U.S. Treasury Inflation-Protected Securities (TIPs) | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total assets	0	0
Convertible securities
Defined Benefit Plan Disclosure [Line Items]
Total assets	$ 12	$ 11
Percent of total assets	3.00%	3.00%
Convertible securities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total assets	$ 12
Convertible securities | Measured using NAV practical expedient
Defined Benefit Plan Disclosure [Line Items]
Total assets		$ 11
Private investment fund—high yield securities
Defined Benefit Plan Disclosure [Line Items]
Total assets	$ 12	$ 11
Percent of total assets	3.00%	3.00%
Private investment fund—high yield securities | Measured using NAV practical expedient
Defined Benefit Plan Disclosure [Line Items]
Total assets	$ 12	$ 11
Other investment—private real estate fund
Defined Benefit Plan Disclosure [Line Items]
Total assets	$ 23	$ 21
Percent of total assets	6.00%	6.00%
Other investment—private real estate fund | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total assets		$ 0
Other investment—private real estate fund | Measured using NAV practical expedient
Defined Benefit Plan Disclosure [Line Items]
Total assets	$ 23	$ 21