Summary of Pre-Tax losses Included in AOCI (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Pension Benefits, Defined Benefit
Summary of the pre-tax losses included in AOCI
Actuarial loss (gain)	$ 1,885	$ 1,762
Prior service credit and transition obligation	(5)	(5)
Total pre-tax loss recognized in AOCI	1,880	1,757
Other Postretirement Benefit Plans, Defined Benefit
Summary of the pre-tax losses included in AOCI
Actuarial loss (gain)	(89)	(107)
Prior service credit and transition obligation	(103)	(94)
Total pre-tax loss recognized in AOCI	$ (192)	$ (201)