Amounts Expected to be Amortized from AOCI to Net Periodic Benefit Cost in 2017 (Detail) $ in Millions	12 Months Ended
Dec. 31, 2016 USD ($)
Pension Benefits, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Actuarial loss/(gain)	$ 162
Total pre-tax amount expected to be amortized from AOCI to net pension and OPEB cost in 2017	162
Other Postretirement Benefit Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Actuarial loss/(gain)	(11)
Prior service credit and transition obligation	(15)
Total pre-tax amount expected to be amortized from AOCI to net pension and OPEB cost in 2017	$ (26)

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