Pension and Other Postretirement Benefits - Narrative (Details) $ in Millions		1 Months Ended	3 Months Ended		6 Months Ended		12 Months Ended
	Jan. 01, 2020 USD ($)	Jun. 30, 2020 USD ($) participants	Jun. 30, 2020 USD ($) participants	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) participants	Jun. 30, 2019 USD ($)	Dec. 31, 2020 USD ($)	Jun. 01, 2020 participants	Apr. 01, 2020 USD ($)	Dec. 31, 2019
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Retirement plans, liability	$ 1,920
Retirement plans, current liability	60
Retirement plans, benefit obligation	4,255
Retirement plans, plan assets	2,335
Establishment of retirement plans, AOCI	$ 1,752		$ 50
Expected employer contributions, 2020		$ 280	$ 280		$ 280
Liability, Defined Benefit Plan, Noncurrent									$ 15
asset, defined benefit plan									$ 65
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate		1.55%	1.55%		1.55%					2.05%
U.K. Defined Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Settlement					$ 250
Forecast
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost							$ 100
Service cost							$ 25
Pension benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost			$ 73	$ 2	94	$ 3
Service cost			5	1	10	1
Multiemployer contribution expense			0	14	0	30
Expected employer contributions, 2020		$ 260	260		260
Other postretirement benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost			6	0	12	0
Service cost			1	0	2	0
Multiemployer contribution expense			0	$ 6	0	$ 11
Expected employer contributions, 2020		55	55		55
Other Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected employer contributions, 2020		10	10		10
U.K. Defined Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Retirement plans, benefit obligation		240	240		240
Retirement plans, plan assets		$ 260	$ 260		$ 260
Defined Benefit Plan, Participants | participants		1,050	1,050		1,050			1,800
Defined Benefit Plan, Plan Assets, Contributions by Employer			$ 10
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Remeasurement due to Settlement			$ 55
U.K. Defined Benefit Plan [Member] | ParentCo
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Participants | participants								3,350
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Settlement		$ 400
Defined Benefit Plan, Plan Assets, Increase (Decrease) for Assets Transferred to (from) Plan		$ 460