Employee Benefits - Components of Net Periodic Benefit Cost (Credit) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Retirement Benefits [Abstract]
Service cost	$ 1	$ 1	$ 2	$ 2
Interest cost	10	13	21	26
Expected return on assets	(26)	(25)	(52)	(51)
Amortization of prior service credit / actuarial loss	5	4	9	7
Net periodic benefit cost	(10)	(7)	(20)	(16)
Settlement charge	0	3		3
Net benefit cost	$ (10)	(4)	$ (20)	(13)
Non-cash pre-tax settlement charge		$ 3		$ 3