Book Values and Fair Values of Financial Instruments (Detail) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Book Values
Fair Value And Carrying Value By Balance Sheet Grouping [Line Items]
Current maturities of long-term debt and lease obligations	$ 3	$ 3
Long-term debt and lease obligations	3,495	3,509
Approximate fair values
Fair Value And Carrying Value By Balance Sheet Grouping [Line Items]
Current maturities of long-term debt and lease obligations	3	3
Long-term debt and lease obligations	$ 3,479	$ 3,595