v3.6.0.2
Postretirement Benefit Plans - Classification of Pension Plan Assets (Detail) - USD ($)
$ in Millions
Dec. 31, 2016
Dec. 31, 2015
Level I [Member]    
Major Funded Pension Plans Postretirement And Other Employee Benefits [Line Items]    
Fair value of plan assets $ 14 $ 10
Level I [Member] | Debt Securities [Member]    
Major Funded Pension Plans Postretirement And Other Employee Benefits [Line Items]    
Fair value of plan assets 9 7
Level I [Member] | Other [Member]    
Major Funded Pension Plans Postretirement And Other Employee Benefits [Line Items]    
Fair value of plan assets 5 3
Level II [Member]    
Major Funded Pension Plans Postretirement And Other Employee Benefits [Line Items]    
Fair value of plan assets 143 152
Level II [Member] | Equity Securities [Member]    
Major Funded Pension Plans Postretirement And Other Employee Benefits [Line Items]    
Fair value of plan assets 48 49
Level II [Member] | Debt Securities [Member]    
Major Funded Pension Plans Postretirement And Other Employee Benefits [Line Items]    
Fair value of plan assets 72 81
Level II [Member] | Insurance Contracts [Member]    
Major Funded Pension Plans Postretirement And Other Employee Benefits [Line Items]    
Fair value of plan assets 12 12
Level II [Member] | Other [Member]    
Major Funded Pension Plans Postretirement And Other Employee Benefits [Line Items]    
Fair value of plan assets 11 10
Level III [Member]    
Major Funded Pension Plans Postretirement And Other Employee Benefits [Line Items]    
Fair value of plan assets 4 3
Level III [Member] | Other [Member]    
Major Funded Pension Plans Postretirement And Other Employee Benefits [Line Items]    
Fair value of plan assets $ 4 $ 3