v3.10.0.1
Postretirement Benefit Plans - Classification of Pension Plan Assets (Detail) - USD ($)
$ in Millions
Dec. 31, 2018
Dec. 31, 2017
Level I [Member]    
Major Funded Pension Plans Postretirement And Other Employee Benefits [Line Items]    
Fair value of plan assets $ 10 $ 12
Level II [Member]    
Major Funded Pension Plans Postretirement And Other Employee Benefits [Line Items]    
Fair value of plan assets 157 163
Level III [Member]    
Major Funded Pension Plans Postretirement And Other Employee Benefits [Line Items]    
Fair value of plan assets 12 8
Equity Securities [Member] | Level I [Member]    
Major Funded Pension Plans Postretirement And Other Employee Benefits [Line Items]    
Fair value of plan assets 0 0
Equity Securities [Member] | Level II [Member]    
Major Funded Pension Plans Postretirement And Other Employee Benefits [Line Items]    
Fair value of plan assets 63 62
Equity Securities [Member] | Level III [Member]    
Major Funded Pension Plans Postretirement And Other Employee Benefits [Line Items]    
Fair value of plan assets 0 0
Debt Securities [Member] | Level I [Member]    
Major Funded Pension Plans Postretirement And Other Employee Benefits [Line Items]    
Fair value of plan assets 9 10
Debt Securities [Member] | Level II [Member]    
Major Funded Pension Plans Postretirement And Other Employee Benefits [Line Items]    
Fair value of plan assets 64 72
Debt Securities [Member] | Level III [Member]    
Major Funded Pension Plans Postretirement And Other Employee Benefits [Line Items]    
Fair value of plan assets 0 0
Insurance Contracts [Member] | Level I [Member]    
Major Funded Pension Plans Postretirement And Other Employee Benefits [Line Items]    
Fair value of plan assets 0 0
Insurance Contracts [Member] | Level II [Member]    
Major Funded Pension Plans Postretirement And Other Employee Benefits [Line Items]    
Fair value of plan assets 14 13
Insurance Contracts [Member] | Level III [Member]    
Major Funded Pension Plans Postretirement And Other Employee Benefits [Line Items]    
Fair value of plan assets 0 0
Other [Member] | Level I [Member]    
Major Funded Pension Plans Postretirement And Other Employee Benefits [Line Items]    
Fair value of plan assets 1 2
Other [Member] | Level II [Member]    
Major Funded Pension Plans Postretirement And Other Employee Benefits [Line Items]    
Fair value of plan assets 16 16
Other [Member] | Level III [Member]    
Major Funded Pension Plans Postretirement And Other Employee Benefits [Line Items]    
Fair value of plan assets $ 12 $ 8