Benefit Plans - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
	Jun. 30, 2014	Sep. 30, 2014
Defined Benefit Plan Disclosure [Line Items]
Eligible age for several postretirement benefit plans		55 years
Eligible age for Medicare benefits		65 years
Gain recognized due to curtailment	$ 86
Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan obligation, discount rate	3.60%
Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan obligation, discount rate	3.10%