Pension - Summary of the Projected Benefit Obligations and Assets Related to Pension Plans (Details) - Pension Benefits - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Change in benefit obligation
Benefit obligation, January 1	$ 5,314	$ 4,741
Service cost	2	2	$ 3
Interest cost	168	194	169
Litigation settlement	0	142
Actuarial losses, net	416	574
Benefits paid from plan assets	(285)	(325)
Benefits paid — other	(15)	(14)
Benefit obligation, December 31	5,600	5,314	4,741
Change in plan assets
Fair value of plan assets, January 1	4,441	4,151
Actual return on plan assets	449	594
Benefits paid	(285)	(325)
Contributions	18	21
Fair value of plan assets, December 31	4,623	4,441	$ 4,151
Funded status	(977)	(873)
Liability in Consolidated Balance Sheets
Accrued expenses and other liabilities	(15)	(18)
Other non-current liabilities	$ (962)	$ (855)