Employee Benefit Plans - Narrative (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Employee Benefit Plans [Line Items]
Increase (decrease) in accumulated other comprehensive gains (losses)	$ (250)	$ (304)	$ 292	$ (294)
Number of days used to compute performance period average closing price of restricted stock units			20 days
RSUs
Employee Benefit Plans [Line Items]
Awards granted (in shares)			2.4
Vesting period			3 years
Time-Vested RSUs
Employee Benefit Plans [Line Items]
Awards granted (in shares)			2.1
Performance-Based RSUs
Employee Benefit Plans [Line Items]
Awards granted (in shares)			0.3
Pension Benefits
Employee Benefit Plans [Line Items]
Special termination benefit	(19)	0	$ (54)	0
Settlement loss for VSPs	$ (319)	0	$ (390)	0
Discount rate	3.01%		3.01%
Increase (decrease) in the projected benefit obligation			$ (380)
Increase (decrease) in accumulated other comprehensive gains (losses)			(286)
Other Postretirement Benefits
Employee Benefit Plans [Line Items]
Special termination benefit	$ (76)	0	(201)	0
Settlement loss for VSPs	$ 0	$ 0	$ 0	$ 0
Discount rate	2.61%		2.61%
Retiree Medical Benefit Program
Employee Benefit Plans [Line Items]
Increase (decrease) in the projected benefit obligation			$ 270
Increase (decrease) in accumulated other comprehensive gains (losses)			$ (69)