Postretirement Plans - Additional Information (Detail) - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Assets set aside expected to be used to pay obligations of defined benefit pension plans and retiree medical and life insurance plans	$ 33,204	$ 33,909
Aggregate liability for postemployment plans	63	70
Actuarial losses and net prior service cost related to postretirement benefit plans expected to be recognized in net periodic benefit cost during 2017	1,200
Actuarial losses and net prior service cost related to postretirement benefit plans expected to be recognized in net periodic benefit cost during 2017, net of tax	800
Expected pension plan expenses during next fiscal year	1,400
Contributions made to defined contribution plans	$ 617	$ 393	$ 385
Shares of our stock held in defined contribution plans we sponsor	36.9	40.0
Non-Qualified Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Defined benefit pension plan, liabilities	$ 1,200	$ 1,200
Assets set aside expected to be used to pay obligations of defined benefit pension plans and retiree medical and life insurance plans	460	421
Unrecognized net actuarial losses	642	632
Benefit plan expense	125	117	115
Unrecognized prior service credit	74	95
Qualified defined benefit pension plans
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation for defined benefit pension plans	44,900	43,500
Accumulated benefit obligation in excess of plan assets	44,800	43,400
Assets set aside expected to be used to pay obligations of defined benefit pension plans and retiree medical and life insurance plans	31,417	32,096	$ 34,673
Unrecognized net actuarial losses	20,184	19,632
Actuarial losses related to postretirement benefit plans expected to be recognized in net periodic benefit cost during 2017	1,100
Actuarial losses related to postretirement benefit plans expected to be recognized in net periodic benefit cost during 2017, net of tax	743
Increase (decrease) in projected benefit obligations due to a change in discount rate	1,400	(2,100)
Contributions made by the employer	23	$ 5
Contributions expected to made by employer in 2017	$ 45