Employee Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 3	$ 3	$ 4	$ 5
Interest cost	4	8	10	14
Expected return on plan assets	(7)	(10)	(16)	(20)
Net amortization	(3)	(1)	(4)	(3)
Net periodic benefit cost	(3)	0	(6)	(4)
UNITED STATES | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	4	4	7	8
Interest cost	23	28	46	55
Expected return on plan assets	(35)	(39)	(70)	(77)
Net amortization	8	7	17	16
Net periodic benefit cost	0	0	0	2
UNITED KINGDOM | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	4	4	8	8
Interest cost	10	13	20	26
Expected return on plan assets	(25)	(25)	(50)	(50)
Net amortization	11	9	21	18
Net periodic benefit cost	$ 0	$ 1	$ (1)	$ 2