Agreements and Transactions with Affiliates - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Operating Expense
Related Party Transaction [Line Items]
Employee related costs	$ 39	$ 49	$ 121	$ 148
General and Administrative Expense
Related Party Transaction [Line Items]
Employee related costs	43	45	113	136
Restructuring costs
Related Party Transaction [Line Items]
Employee related costs	$ 0	$ 2	$ 9	$ 11