Supplemental Cash Flow Information (Summary of Reconciliation of Additions to Property, Plant and Equipment to Total Capital Expenditures) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Supplemental Cash Flow Elements [Abstract]
Increase/(decrease) in capital accruals	$ (146)	$ 135	$ 71