Employee Benefit Plans (Schedule of Fair Value Measurements By Category) (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Total assets in the fair value hierarchy	$ 725	$ 677	$ 781
Common collective trust	311	373
Joint venture interests	0	77
Total investments	725	677
Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Total assets in the fair value hierarchy	414	227
Fair Value, Inputs, Level 2 | Mutual Funds
Defined Benefit Plan Disclosure [Line Items]
Total assets in the fair value hierarchy	152	99
Fair Value, Inputs, Level 2 | Short-term Investments
Defined Benefit Plan Disclosure [Line Items]
Total assets in the fair value hierarchy	0	19
Fair Value, Inputs, Level 2 | US Treasury securities
Defined Benefit Plan Disclosure [Line Items]
Total assets in the fair value hierarchy	3	7
Fair Value, Inputs, Level 2 | Corporate Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Total assets in the fair value hierarchy	233	86
Fair Value, Inputs, Level 2 | Government and Other Debt Instruments
Defined Benefit Plan Disclosure [Line Items]
Total assets in the fair value hierarchy	$ 26	$ 16