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Pension and Other Postretirement Benefits - Reconciliation of Fair Value Measurements Using Significant Unobservable Inputs (Detail) - Significant Unobservable Inputs (Level 3) [Member] - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]    
Fair value of plan assets at beginning of year $ 12 $ 12
Transfer in (out) of Level 3 0 0
Purchases 0 0
Sales 0 0
Settlements (1)  
Unrealized gain (loss) 0 0
Realized gain 0 0
Fair value of plan assets at end of year 11 12
Equity Securities [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Fair value of plan assets at beginning of year 1 1
Transfer in (out) of Level 3 0 0
Purchases 0 0
Sales 0 0
Unrealized gain (loss) 0 0
Realized gain 0 0
Fair value of plan assets at end of year 1 1
Fixed Income [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Fair value of plan assets at beginning of year 11 11
Transfer in (out) of Level 3 0 0
Purchases 0 0
Sales 0 0
Settlements (1)  
Unrealized gain (loss) 0 0
Realized gain 0 0
Fair value of plan assets at end of year $ 10 $ 11