Leases - Summary of Lease Assets and Liabilities (Detail) $ in Millions	Sep. 30, 2019 USD ($)
Schedule Of Assets And Liabilities Lessee [Line Items]
Total lease liabilities	$ 29
Other Deferred Debits [Member]
Schedule Of Assets And Liabilities Lessee [Line Items]
Right-of-use asset	28
Other Current Liabilities [Member]
Schedule Of Assets And Liabilities Lessee [Line Items]
Current	1
Deferred Credits and Other Liabilities [Member]
Schedule Of Assets And Liabilities Lessee [Line Items]
Long-term	$ 28