Postretirement Benefit Plans - Additional Information (Detail) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Liability related to funded defined-benefit pension plans	$ 394	$ 403
Contributions to benefit plans	12
Insurance cash value and Rabbi Trust investments supporting supplemental pension plan liability	78	74
Non-qualified supplemental retirement pension plan liability	73	$ 71
Maximum [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected contributions in current fiscal year	$ 20