XML 78 R64.htm IDEA: XBRL DOCUMENT v3.7.0.1
Components of Net Periodic Postretirement Health Care Costs (Parenthetical) (Detail) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2017
Jun. 30, 2017
Defined Benefit Plan Disclosure [Line Items]    
Gain related to a change in the eligibility requirement and a change in benefits to Medicare-eligible participants $ 8 $ 16