Benefit Plans - Estimated Amounts to be Recognized from AOCI into Net Periodic Cost (Benefit) (Detail) $ in Millions	12 Months Ended
Dec. 31, 2016 USD ($)
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Amortization of net actuarial (gain) loss	$ 43
Total estimated amounts to be recognized	43
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Amortization of net actuarial (gain) loss	(1)
Amortization of prior service credit	(2)
Total estimated amounts to be recognized	$ (3)

Amount included in accumulated other comprehensive income (AOCI) 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, including gain (loss), prior service cost (credit), and transition asset (obligation).

No definition available.

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