Revenue Recognition Contract Assets (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2017
Revenue Recognition [Abstract]
Contract with Customer, Asset, after Allowance for Credit Loss	$ 31	$ 56	$ 31	$ 56	$ 17	$ 4	$ 39	$ 4
Contract with Customer, Asset, Cumulative Catch-up Adjustment to Revenue, Change in Measure of Progress	14	17	53	53
Contract with Customer, Asset, Reclassified to Receivable	$ 0	$ 0	$ (26)	$ (1)