Employee Benefit Plans (Schedule of Fair Value Measurements By Category) (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Total assets in the fair value hierarchy	$ 360	$ 414
Common collective trust	387	311
Total investments	747	725
Fair Value, Inputs, Level 1 | Cash and Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Total assets in the fair value hierarchy	10	3
Fair Value, Inputs, Level 2 | Mutual Funds
Defined Benefit Plan Disclosure [Line Items]
Total assets in the fair value hierarchy		152
Fair Value, Inputs, Level 2 | Corporate Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Total assets in the fair value hierarchy	315	233
Fair Value, Inputs, Level 2 | Government and Other Debt Instruments
Defined Benefit Plan Disclosure [Line Items]
Total assets in the fair value hierarchy	$ 35	$ 26