Amortized Accumulated Other Comprehensive Income (Loss) Into Net Periodic Benefit Cost (Detail) $ in Millions	12 Months Ended
Dec. 31, 2016 USD ($)
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Actuarial (gain) loss	$ 127
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Actuarial (gain) loss	(36)
Prior service credit	$ (37)

Amount included in accumulated other comprehensive income (AOCI) related to prior service cost (credit) expected to be recognized as components of net periodic benefit cost for the fiscal year that follows the most recent annual statement of financial position.

No definition available.

Name:	us-gaap_DefinedBenefitPlanFutureAmortizationOfPriorServiceCostCredit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration