Retirement Benefits - Narrative (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Compensation and Retirement Disclosure [Line Items]
Portion of pension and OPEB obligation attributed to disclosed plans (as a percent)			99.00%
Defined contribution plan, employer contribution	$ 40,000,000	$ 37,000,000	$ 83,000,000	$ 78,000,000
Pension Plan [Member] | United States [Member]
Compensation and Retirement Disclosure [Line Items]
Defined benefit pension plans, employer contributions			0
Defined benefit plan, estimated future employer additional contributions, remainder of fiscal year	18,000,000		18,000,000
Pension Plan [Member] | United Kingdom [Member]
Compensation and Retirement Disclosure [Line Items]
Defined benefit pension plans, employer contributions			35,000,000
Defined benefit plan, estimated future employer additional contributions, remainder of fiscal year	30,000,000		30,000,000
Pension Plan [Member] | Other Foreign Plans [Member]
Compensation and Retirement Disclosure [Line Items]
Defined benefit pension plans, employer contributions			17,000,000
Defined benefit plan, estimated future employer additional contributions, remainder of fiscal year	$ 5,000,000		$ 5,000,000