Debt - Other Outstanding Letters of Credit (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Line Of Credit Facility [Line Items]
Other outstanding letters of credit	$ 272	$ 284
Committed Lines
Line Of Credit Facility [Line Items]
Other outstanding letters of credit	54	29
Uncommitted Lines
Line Of Credit Facility [Line Items]
Other outstanding letters of credit	$ 218	$ 255