Health Care, Pension and Other Benefits - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Dec. 31, 2018	Sep. 30, 2018
Forecast
Defined Benefit Plan Disclosure [Line Items]
Settlement charge recognized	$ 20
Minimum
Defined Benefit Plan Disclosure [Line Items]
Expected total settlement charge		$ 41
Maximum
Defined Benefit Plan Disclosure [Line Items]
Expected total settlement charge		$ 61