Employee Benefits - Components of Net Periodic Benefit Cost (Credit) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Retirement Benefits [Abstract]
Service cost	$ 1	$ 1	$ 3	$ 3
Interest cost	10	13	31	39
Expected return on assets	(26)	(26)	(78)	(76)
Amortization of prior service credit / actuarial loss	5	4	13	10
Net periodic benefit cost	(10)	(8)	(31)	(24)
Settlement charge	0	0	0	3
Net benefit cost	$ (10)	$ (8)	$ (31)	(21)
Non-cash pre-tax settlement charge				$ 3