Employee Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1	$ 1	$ 6	$ 6
Interest cost	6	7	20	19
Expected return on plan assets	(10)	(9)	(30)	(31)
Net amortization	0	(3)	(3)	(9)
Net periodic benefit cost	(3)	(4)	(7)	(15)
UNITED STATES | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	4	5	12	15
Interest cost	27	26	82	78
Expected return on plan assets	(38)	(41)	(115)	(123)
Net amortization	8	8	24	23
Net periodic benefit cost	1	(2)	3	(7)
UNITED KINGDOM | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	3	5	11	15
Interest cost	13	14	39	42
Expected return on plan assets	(24)	(25)	(74)	(78)
Defined Benefit Plan, Accumulated Benefit Obligation, (Increase) Decrease for Settlement and Curtailment	21	12	21	36
Net amortization	9	9	27	38
Net periodic benefit cost	$ 22	$ 15	$ 24	$ 53