Retirement and Postretirement Benefit Plans - Components of Net Periodic Benefit Costs (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
	Aug. 08, 2019	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Net Periodic Benefit Costs
Accumulated other comprehensive income eliminated in purchase price accounting	$ 390
Pension Benefit
Net Periodic Benefit Costs
Increase in benefit obligation from remeasurement	$ 193
Curtailment gain		$ 34		$ 10
Net periodic benefit cost		15	$ 2	19	$ 4
Employer contributions		7	2	8	4
Postretirement Benefit
Net Periodic Benefit Costs
Net periodic benefit cost		$ 19	$ 15	$ 48	$ 55