Benefit Plans (Components of net periodic cost (benefit)) (Details) - Pension Benefits - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Interest cost on projected benefit obligation	$ 80	$ 100	$ 93
Expected return on plan assets	(155)	(142)	(159)
Amortization of net actuarial (gain) loss	45	39	37
Settlement loss	3	0	6
Total net periodic pension cost (benefit)	$ (27)	$ (3)	$ (23)