Employee Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1	$ 1	$ 5	$ 6
Interest cost	6	6	16	20
Expected return on plan assets	(9)	(10)	(25)	(30)
Net amortization	(1)	0	(5)	(3)
Net periodic benefit cost	(3)	(3)	(9)	(7)
UNITED KINGDOM | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	4	3	12	11
Interest cost	10	13	30	39
Expected return on plan assets	(26)	(24)	(76)	(74)
Settlement	0	21	0	21
Net amortization	11	9	32	27
Net periodic benefit cost	(1)	22	(2)	24
UNITED STATES | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	4	4	11	12
Interest cost	23	27	69	82
Expected return on plan assets	(35)	(38)	(105)	(115)
Net amortization	8	8	25	24
Net periodic benefit cost	$ 0	$ 1	$ 0	$ 3