Benefit Obligations (Pension and Other Postretirement Obligations Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Multiemployer plans, funded status	At least 80 percent	At least 80 percent	At least 80 percent
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Curtailment gain (loss)	$ 0	$ 1	$ 0
Amortization of prior service cost (credit)	0	0	0
Lump-sum buyout payments	3	0
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Curtailment gain (loss)	0	0	0
Amortization of prior service cost (credit)	0	0	$ (1)
Lump-sum buyout payments	$ 0	$ 0