Employee Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2	$ 1
Interest cost	5	6
Expected return on plan assets	(5)	(9)
Net amortization	(1)	(1)
Net periodic benefit cost (credit)	1	(3)
UNITED STATES | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	7	3
Interest cost	20	23
Expected return on plan assets	(33)	(35)
Net amortization	6	9
Net periodic benefit cost (credit)	0	0
UNITED KINGDOM | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	4	4
Interest cost	8	10
Expected return on plan assets	(28)	(25)
Net amortization	14	10
Net periodic benefit cost (credit)	$ (2)	$ (1)