Employee Pension and Other Postretirement Benefits - Periodic Benefit Costs, Forecasted (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pension Plan and Other Postretirement Benefits Plan
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		$ 16,580	$ 18,355	$ 17,386	$ 16,593
Amortization period of net actuarial losses		8 years
Excess of market value of plan assets		$ 214
Assetsmoothingperiodofnonamortizing amount		4 years
Pension Benefits
Pension Plan and Other Postretirement Benefits Plan
Net actuarial loss, Gross		$ (1,036)	$ (905)
Actuarial loss, subject to amortization		$ 447
Expected return on plan assets		8.00%	8.00%
Rate of increase in future compensation levels for determining net periodic benefit cost		5.00%	5.00%
Net periodic benefit cost		$ (27)	$ (31)	$ 16
Prior service costs (credits), Gross		$ (126)	$ (152)
Pension Benefits | Forecast
Pension Plan and Other Postretirement Benefits Plan
Assumptions used to calculate net periodic benefit cost, service cost rate	4.19%
Defined benefit plan, assumptions used calculating net periodic benefit cost, interest cost	3.90%
Expected return on plan assets	7.00%
Rate of increase in future compensation levels for determining net periodic benefit cost	5.10%
Net periodic benefit cost	$ 27
Effect of 50 basis point increase on discount rate	25
Effect of 50 basis point increase on expected rate of return	18
Effect of 50 basis point increase on future compensation levels	1
Effect of 50 basis point decrease on discount rate	27
Effect of 50 basis point decrease on expected rate of return on plan assets	18
Effect of 50 basis point decrease on future compensation levels	$ 1