Revenue from Contracts with Customers - Contract Balances (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Change in Contract with Customer, Asset and Liability [Abstract]
Contract Assets	$ 63	$ 51
Contract Liabilities	560	645
Change in contract assets included in other current assets	12
Change in contracts liabilities included in deferred revenue	(85)
Current portion of contract assets	50	51
Amounts included in the beginning of year contract liability balance	$ 643	$ 710