Employee Benefit Plans - Narrative (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Employee Benefit Plans [Line Items]
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	$ (35)	$ 0	$ (35)	$ 0
Settlement loss for VSPs	$ (71)	0	$ (71)	0
Discount rate	3.24%		3.24%
Increase (decrease) in the projected benefit obligation			$ 655
Other Postretirement Benefits
Employee Benefit Plans [Line Items]
Special termination benefit	$ (125)	0	(125)	0
Settlement loss for VSPs	$ 0	$ 0	$ 0	$ 0
Discount rate	2.73%		2.73%
Increase (decrease) in the projected benefit obligation			$ 65