Revenue Recognition Contract Liabilities (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Contract With Customer, Liability [Line Items]
Contract with Customer, Liability - Beginning of Period	$ 1,215	$ 1,397
Contract with Customer, Liability, Cumulative Catch-up Adjustment to Revenue, Change in Measure of Progress	28	33
ContractLiabilityNoncashInterestExpenseSignificantFinancingObligation	3	4
Contract with Customer, Liability, Revenue Recognized	(57)	(99)
Contract with Customer, Liability - End of Period	$ 1,189	$ 1,335