Employee Benefit Plans - Change Plan Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Pension Benefits
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets — beginning of year	$ 3,344	$ 3,592
Actual return on plan assets	701	(172)
Employer contributions [1]	70	103
Benefits paid	(176)	(161)
Expenses paid	(26)	(17)
Foreign exchange adjustment	1	(1)
Fair value of plan assets — end of year	3,914	3,344
Funded status — end of year	(584)	(656)
Other Postretirement Benefits
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets — beginning of year	85	114
Actual return on plan assets	12	(2)
Employer contributions [1]	0	0
Benefits paid	(22)	(27)
Expenses paid	0	0
Foreign exchange adjustment	0	0
Fair value of plan assets — end of year	75	85
Funded status — end of year	$ (148)	$ (135)