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Employee Retirement Benefits - Components of Net Periodic Costs for Qualified and Supplemental Pension Plans (Detail) (Qualified Pension Plans [Member], USD $)
In Millions, unless otherwise specified
3 Months Ended 9 Months Ended
Sep. 30, 2014
Mar. 31, 2014
Sep. 30, 2013
Sep. 30, 2014
Sep. 30, 2013
Qualified Pension Plans [Member]
         
Defined Benefit Plan Disclosure [Line Items]          
Service cost $ 3   $ 4 $ 8 $ 10
Interest cost 4   4 11 10
Expected return on plan assets (5)   (5) (13) (13)
Amortization of actuarial loss and prior service cost 1   2 2 7
Net periodic benefit cost 3   5 8 14
Pension contributions   5      
Expected contributions by employer in the remainder of year $ 0     $ 0